FIFTY YEARS OF DARWINISM

MODERN A SPECTS OF EVOLUTION

CENTENNIAL ADDRESSES IN HONOR OF CHARLES DARWIN

Before the American Association for the Advancement of Science, Baltimore, Friday, January 1, 1909

NE\V YORK

HENRY HOLT AND COMPANY 1909

t

CoPVRtORT, 1909,

BY

HENRY HOLT AND COMPANY

Pu/Jli8/Ud .AprU, 1909

HIITORICAI. ll• DICAI.

< I .Q l'I t,. \1-..\o

l

TRE QUINN & BODEN' CO, PRESS llAl-lWAY, N, 1,

CONTENTS PAGE

IN'fRODUCTION 1 T. C. C1IAMDIERLJN, University of Chicago

FIFTY YEARS OF DARWINISM . 8 EowA1tD B. PoULTON, Oxford University

THE THEORY OF NATURAL SELECTION FROM THE STANDPOINT OF BOTANY . 57

JonN 111. CouLTER, University of Chicago

ISOLATION AS A FACTOR IN ORGANIC EVOLU-TION 79

DAvro STARR JORllAN, Stanford University

T HE CELL IN RELATION TO H EREDITY AND EVOLUTION 9'1

EDMUND B. ,vu.soN, Columbia University

THE DIRECT INFLUENCE OF ENVIRONMENT 114

D. T. Jl,JAcDouGAL, Carnegie Institution of \Vash­ington

THE BEHAVIOR. OF UNIT CHARACTERS IN HEREDITY 143

,v. E. CASTLE, Harvard University

:MUTATION 160 CHAS. B. D.AVENP001·, Carnegie Institution of

\Vashington

ADAPTATION 18,l CARL H. EroEN:trANN, Indiana University

DARWIN AND PALEONTOLOGY . '109 HENRY FAmFrELO Osnoo:s, Columbia University

and American Museum of Natural History

EVOLUTION AND PSYCHOLOGY . 251 G. STANLEY HALL, Clark University

iii

PLATES PLATE I

Fig. 1. Leptinotarsa undecimlineata, normal form.

Fig. 2. Form derived from L. undlecimlineata through

the application of the climntic conditions.

Figs. S, 4. Normal mitosis of nuclei in cells of plant.

Figs. 5, 6, 1, 8. Irregularities of mitosis in cells o:f

onion roots resulting from exposure to radium.

[After Gager.]

l i5

PLATE II 133

T. T. Upper and lower aspects of rosette of CEMthera biennis.

D. D. Rosette of derivative resulting from ovarial treatment with zinc sulphate.

PLATE III. A FEW' OF THE NUMEROUS TYPES OF TEETH IN

TH£ CHARACINS 19,!

'PLATE IV. so~IE SIMILARITIES IN THE CH,\JIACllS'S 192

PLATE V .

RECTIGllADATIONS IN THE TEETH OF EOCENE UNGULATES.

ToP VIEW OF THREE SKULLS or EocENE TITANOTHERES

Ju,US'l'll-"'TINO BRACHYCEPHALY, MESATlCEPHALY, AND

DoucnoCEPRALY RESPECTll'ELY.

245

IN TROD UCTION BY

T . C. CHAMBERLIN

THE greatness of a man is sho,vn in " 'hat he is, in ,vhat he does, and in ,vhat he sets a-doing.

I f the long list of contributions to the sessions of this Association have been, for these fifty were searched for products of thought whose stimulus sprang from the life and works of Charles D arwin, it ,vould reveal an impressive testimonial to his greatness as a po,ver in our scientific ,vorld. I f it ·were possible to give such an intellectual product a material embodiment and an approp1·iate form, we could raise no more sincere monument to his memory. Even in the less tangible form it inevitably bears, it is our monument. .By responses, individual and col­lective, to the marvelous suggestiveness of D ar­win's inquiries and interpretations, the members of this Association during the last half century years, paying tlheir truest tributes. More or less unconsciously, no doubt, but none the less gen­uinely, we have thus been doing honor to one of the greatest of intellectual leaders.

The magnitude of any moving force is meas­w·ed scarcely less by the obstacles surmounted

INTRODUCTION

and by the inertia overcome than by the positive momentum it generates. In the first decades of the great Dar,vinian movement in biology, the tribute of our members may not have been want­ing in demonstrations of the force of old adhe­sions, but even then, whether by resistance or by cooperation, ,ve gave our testimony to the new power that made itself felt in the scientific world. A little later ,ve paid the tribute of conviction­the general tribute of "villing conviction, on the part of some of us, and the even more significant tribute of reluctant conviction, on the part of others; but, in one way or another, ·we paid a uni­versal tribute.

If we of the older school permit ourselves to be reminiscent, the tides of thought and feeling of the early days of the half century we celebrate easily surge back into consciousness. vVe readily recall the stirrings in the biological field when the great question of derivation of species arose into a concrete and, as it seemed to some, a threaten­ing form. But it was not among us as biolo­gists, but an1ong us as members of a proud race, that emotion was deepest stirred. It was in the humanistic atmosphere that protests ,vere most vibrant, for man-scientific man not excepted­is first of all a creature ,vho takes thought of him­self. His anthropic pride, fostered by tradi­tional assumptions of separateness and eminent superiority- assumptions peculiar to no race, nation, or religion, but the corrunon inheritance

INTRODUCTION 3

of us all-rose up in remonstrance and put bar­riers in the way of a candid reception of the ne,v interpretations. But still, with all his foibles, man, at least man of t he better sort, proclaims adhesion to the ancient admonition, " l{now thy­self," and ultimately he strives to be loyal to the intellectual precedence he assigns himself. It is his to know the truth. Those of scientific trend early found occasion to call into fresh activity the maxim that it is better to accept the truth than to think of ourselves more highly than we ought to think. Whatever ruffiings of our fond sense of humanistic caste were felt from the new interpretations in those first days of disturbed equanimity, we soon came to find complacency in the new place assigned us at the head of a multitudinous kin, the place of leadership in the van of a great procession of ascending tribes striving for supreme fitness.

But the days of disturbed tranquillity, for us of the scientific household at least, soon passed away; and, if they linger with any still, it can only be among those outside the wide limits of this Association. W e are yet far from kno,ving the whole truth, but we are tranquil in the search for it, welcome or unwelcome as it may prove at first to be.

I n the later decades of this memorable half century, the tribute of our membership, indi­vidual and coI!ective, has lain in attempts to extend, to amend, to qualify, and to apply the

4 I NTRODUCTION

parent thought to which Darwin gave such pro­digious impetus. To what result we have labored to add to, or to subtract from, his great concep­tion, the future must decide. The effort is our tribute to the power that has moved us.

The biological realm was indeed the center of the great .movement. Of this central movement and of the varied lines into which it has deployed, ,ve shall learn through the " 'ords of those who are entitled to speak. T o these, in a moment, I shall give place. But, though the revolution had its origin in the biological field, it was by no means limited to it. It soon became a radiant influence so penetrating and so stimulating that it has been felt in ever y field of thought. No realm of the intellectual world has failed to re­spond to the power of D arwin's method, the can­dor of his spirit, and the force of his clear insight and restrained judgment.

Dar,vin not only gave f orn1 to the whole trend of evolutionary inquiry, but he chastened and re­fined the moral aspects of thought in all lines of serious intellectual endeavor. I t ,vould be too much to say that he was the father of the evolu­tionary conception or the sole parent of the chastened moral attitude of thought no,v felt to be binding in the scientific ,vorld. ,iV e would do him a dishonor most obnoxious to his candid and truthful spirit if we were to assign hin1t n1ore than historic tr uth amply warrants. , iV e must not fail to recognize that before his time the evolu-

INTRODUCTION 5

tionary conception had found place in the thought of not a f e,v philosophic inquirers, not the least among ,vhon1 ,vas one of his o'l-vn lineage; but yet it ,vas Charles Dar,vin, more than any other, who gave definiteness and concreteness, ·who gave method and spirit, to the doctrine of derivation, and ,vho thus became parental to the great 1nove­ment in a sense equaled by no other. Such ac­ceptances of evolutionary conceptions as had much currency before his day, or had much tangible influence on research, were cosmogonic rather than biologic. Beyond doubt these pioneer gropings in the less biased fields prepared the ,vay for his great contribution, but they did not equally encounter the central obstacle that lay in inherited adhesions and traditional preposses­sions, and they did not, therefore, and could not, equally revolutionize the spirit and the attitude of the thinking ,vorld by touching with trans­forming power the mainspring of bias.

But if Darwin found some measure of prep­aration for his ,vork in the labors of predecessors in his own and other fields, he more than amply repaid the debt. The stimulative influence of Dar,vinism on fundamental conceptions in the celestial and terrestrial kingdoms follo,ved close on those in the biological realm. Both terrestrial and celestial history are even no,v in the flux of reinterpretation. The sources of this revision of vie,v are indeed various, but a profound Dar­"vinian influence is felt in it all. It " ·ould have

6 INTRODUCTION

been felt had Darwin left nothing but his Origin of Species and the remarkable trea­tises that f ollo,ved it, but he has added thereto leaders of thought of his own name and lineage, and they have carried his spirit and his breadth of view into realms he could not himself enter. The evolution of the earth and of the heavens has thus felt his tr ansmitted touch. The concept of kinship of worlds follows eas­ily on the concept of the kinship of organic beings.

In the transformed attitude of the intellectual world to-day, the mooted question of the hour­the evolution of t he atom-finds a fair field, wherein evidence needs but to accredit itself duly to have its place and weight freely accorded it. I f the atom shall sho,v an authenticated pedigree, it will easily t ake its place in the procession of the derived, with the plant, the animal, the earth, and the stars.

The contributions of D ar,vin to the science which it has fallen to me to follow have been great and various, but the greatest of them all relate to the history of life on the globe. The geolog­ical record, as known in his day, was at once a foundation for his work and an obstacle to its acceptance. It was the mission of his interpre­tations to bring forth the added truth which made the foundation broader and firmer, and ,vhich not only removed the seeming obstacles in the evolu­tionary path, but replaced them by cogent evi-

INTRODUCTION 7 •

dence of the continuity of life and of its successive steps of progress.

But it does not fall to me to enter upon any of the special fields to which Darwin made his mon­umental contributions. Your committee has ,visely assigned the leading aspects of the theory of evolution to those peculiarly fitted to treat them by reason of their own high attainments. In this introductory word on behalf of the Asso­ciation, I have found no more fitting way to ex­press our appreciation than to recall the tribute we have been paying by what ,ve have done, and what we are trying to do, because Darwin set us a-doing.

}'IFTY YEARS OF DARWIN ISM

BY

ED,VARD B. POULTON

ON this historic occasion it is of special interest to reflect for a fe,v moments on the part played by the New ,v orld in the origin and gro,vth of the gr.eat intellectual force ,vhich dominates the past half century. The central doctrine of evo­lution, quite apart f ro1n any explanation of it, was first forced upon Darwin's mind by his South American observations during the voyage of the Beagle; and ,ve may be sure that his experience in this same country, teeming ,vith innumerable and varied forms of life, confirmed and deepened his convictions as to the importance of adaptation and thus prepared the ,vay for Natural Selection. vVallace, too, at firsit traveled in South America; only later in the par ts of the Old \V orld tropics ,vhich stand next to South A.inerica in richness.

Asa Gray in the N e,v World represented Sir Joseph Hooker in the Old, as regards the help given to Dar,vin before the appearance of the 01-igin, and in strenuous and most efficient de­fense after its appearance. Chauncey v\Tright similarly represents l-Ienry Fa,vcett. Fritz ~fuller not only actively defended Dar,vin, but

8

FIFTY YEARS OF DARWI NISl\<I 9

continually assisted him by the most admirable and original observations carried out at his Bra­zilian home. Turning to those ,vho in some im­portant respects differed from Dar,vin, I do not think a finer example of chivalrous controversy can be found than that carried on between him and H yatt. The immense growth of evoluti~n­ary teaching, in which John Fiske played so im­portant a part, although associated with the name of Herbert Spencer, must not be neglected on an occasion devoted to the memory of Dar,vin.

Outside the conflict ,vhich raged around the Origin, we find Dana, the only naturalist who at first supported Dar,vin in his views on the per­sistence of ocean basins and continental areas, and Alexander Agassiz, for many years the principal defender of the Darwinian theory of coral islands and atolls.

American paleontology, famed throughout the world, has exercised a profound influence on the growth and direction of evolutionary thought. The scale and perfection of its splendid fossil records have attracted the services of a large band of the most eminent and successful laborers, of whom I can only mention the leaders :- Leidy, Cope, Marsh, Osborn, and Scott in the Ver­tebrata; Hall, Hyatt, and Walcott in the Inver­tebrate sub-kingdom. The study of American paleontology was at first believed to support a Neo-Lamarckian view of evolution, but this, as well as the hypothesis of polyphyletic origins,

10 FIFTY YEARS OF DARWINISM

,vas und,ermined by the teachings 0£ W eismann. Difficulties for ,vhich the Lamarckian theory had been invoked were met by the hypothesis of Organic Selection suggested by Baldwin and Osborn, and in England by Lloyd Morgan. '1Veismann's contention that inherent characters are .. alone transmissible by heredity has also re­ceived strong support from the immense body of cytological, Mendelian, and mutationist work to which the present volume bears such eloquent tes­timony. Finally, the flourishing school of Amer­ican psychology, under the leadership of William James and James l\{ark Bald\\rin, accepts, and in accepting helps to connrm, the theory of Natural Selection.

ERASl\.fUS DARWIN AND LAl\1ARCK

Professor Henry F. Osborn, in his interest­ing wo1·k From the Greeks to Darwin, con­cludes tl1at Lamarck was unaware of Erasmus Dar\vin's Zoonomia, and that the parallelism of thought is a coincidence.' The following passage from a letter 2 ,vritten to Huxley probably in 1859, and published since the appearance of Pro­fessor Osborn's book, indicates that Charles Dar­·win suspected the French naturalist of borrowing from his grandfather:-

• F.-om the Greeks to Da,i~oili, New York, 1894-, pp. 15i-55. Pro­fessor Osborn shows that on p . 14-5 Erasmus Darwin macle use of the term "acquired" in the sense of "acquired characters"; " changeroent aequis" is the form employed by Laroarck.

'More Letters of Cllarles Darwin, I, p. 125.

FIFTY YEARS OF DARWINISM 11

" T he history of error is quite unimportant, but it is curious to observe how ei.actly and accurately my grandfather (in Zoonomia, Vol. I , p. 504, 1794) gives Lan1arck's theory. I will quote one sentence. Speaking of birds' beaks, he says : ' All which seem to have been gradually produced during many generations by the perpetual endeavor of the creatures to supply the want of food, and to have been delivered to their posterity witl1 constant imp1·ovement of them for the purposes required.' L amarck published Hist. Zool,og. in 1809. T he Zoonomia was translated into many languages.''

A careful comparison of the French t ransla­tion of the Z oonomia ·with L amarck's Philosophie Z oologiqu,e and 'with a preliminary statement of his vie\vs published in 1802, would probably de­cide this interesting question.

THE INFLUENCE OF LYELL UPON CHARLES DAR\<VIN •

T he limits of space compel me to pass by the youth of Charles Darwin, with the influence of school, Edinburgh and Cambridge, including the intimacy with H enslow and Sedgwick-friend­shi ps leading to his voyage in the B eagleJ an event ,vhich more than any other determined his whole career. We must also pass by his earliest convictions on evolution, the first note-book begun in 1837, the reading of Malthus and discovery of Natural Selection in October, 1838, the imper­fect sketch of 1842, the completed sketch of 1844.

I t is necessary, however, to pause for a brief consideration of the influence of Sir Charles

1~ FIFTY YEARS OF DARWINISl\1

Lyell. Although the ,vritings of the illustrious geologist have ahvays been looked upon as among the greatest of the forces brought to bear upon the mind of Darvvin, evidence derived from the later volumes of correspondence justifies the be­lief that the effect ,vas even greater and more sig­nificant than has been supposed.

Huxley has maintained ,vith great force that the way was paved for D.arwin by Lyell's Prin­ciples of Geology far more thoroughly than by any other ,vork.

" . . . Consistent uniforroitarianism postulates evo­lution as much in the organic as in the inorganic world. The origin of a new species by other than ordi­nary agencies would be a vastly greater ' catastrophe' than any of those which Lyell successfully eliminated from sober geological speculation." 1

When the Principles nrst appeared Dar-~vin "\-Vas advised by I-Ienslo,v to obtain and study the first volun1e, " but on no account to accept the vie"\-vs therein advocated." But a study of the very first place at ·which the B eagle touched, St. Iago, one of the Cape de Verde Islands, sho,\·ed Da1·,vin the infinite superiority of Lyell's teach­ings. H e wrote to L. Horner, 2 August 29, 1844:-

. " I have been lately reading with care A. d'Orbigny's work on South America, and I cannot say how forcibly impressed I am with the infinite superior!ty of the Lyellian school of Geology over the continental. I

• Life and Letters of Clia?'les Danoi1t, II, p. 190. • llfore Letters, II, p. 117.

FIFTY YEARS OF DAR,VINIS:i\-1 18

always feel as if my books came half out of Lyell's brain, and that I never acknowledge this sufficiently; nor do I know how I can without saying so in so many wo1·ds­for I have always thought that the great merit of the Principles was that it altered the whole tone of one's mind, and therefore that, when seeing a thing never seen by Lyell, one yet saw it partially through his eyes - it would have been in some respects better if I had done this Jess, . . . "

This letter ,vas ·written a few weeks after the date, July 5, 1844, v.rhich marks the completion of the finished sketch of that year. On July 5 Dar,vin ,vrote the letter to his ,vife begging her, in the event of his death, to arrange for the pub­lication of the account he had just prepared. At this psychological moment in his career he vvrote of the influence received from Lyell, and we are naturally led to observe how essentially Lyellian are the three lines of argument-t,vo based on geographical distribution, one on the relation be­t",,een the living and the dead- which first led Darwin toward a belief in evolution! The thought ,vhich shook the world arose in a mind ,vhose ,vhole tone had been altered by Lyell's teachings. Inasmuch as the founder of modern geology received his first inspiration fron1 .Buck­land, Oxford m:ay claim some share in moulding the mind of Darwin.

"COMING EVENTS CAST THEIR SHADO\VS BEFORE"

The characteristic feature in ,vhich Natural Selection differs from every other attempt to

14 FIFTY YEARS OF DAR,VI NISM

solve the problem of evolution is the account taken of the struggle for existence, and the role assigned to it. This struggle is keenly appre­ciated in T ennyson's noble poem, I n Memoria1n, the dedication of ,vhich is dated 1849, ten years before the Origin. Tihe poet is disquieted by:-

and by "

" Nature red in tooth and claw W 'tl . " 1 1 ravine, . . .

finding that of fifty seeds She often brings but one to grow."

It is interesting to n ote that the obvious under­statement of this last passage is corrected in the author's notes published by his son a few years ago. I n these ,ve find for " fifty" read "myriad." The poignant sense of the ,vaste of individual lives is brought into close relation in the poem with the destruction of the type or . species:-

" So careful of the type she seems, So careless of the single life;

• ' So careful of the type '? but no,

From scarped cliff and qua1Tied stone She cries ' A thousand types are gone:

I care for nothing, all shall go.' "

I n this association between the struggle for existence waged by individuals and the extinction and succession of species ,ve seem to approach the central idea of D ar,vin and Wallace. I asked Dr. Grove of Newport in the Isle of Wight if he

FIFTY YEARS OF DARWINISM 15

would point out the parallelism, so far as it ex­isted, to his illustrious patient, hoping that some light might be thrown on the source of the in­spiration. Nor was I disappointed. "Stay," said the aged poet ·when Dr. Grove had spoken, " I n JJi e1no1·iavi was published long before the 01igin of Species." "Oh! Then you are the man," replied the doctor. "Yes, I am the man." There was silence for a time and then Tennyson said: " I don't want you to go away with a wrong impression. The fact is that long before D ar­"vin's ,vork appeared these ideas were kno,vn and talked about." From this deeply interesting conversation I think it is probable that, through mutual friends, some echo of Darwin's researches and thoughts had reached the great author of In ll'I e1noria1n.

The light which has been recently thrown 1 upon P hilip Gosse's l'emal'kable book, Omphalos, indi­cates that its appearance in 1858 was connected with the thoughts that were to arouse the world in the following year. The author of Oniphalos ,vas a keen and enthusiastic naturalist held fast in the grip of the narrowest of religious creeds. We learn with great interest that he and others were by Lyell's advice prepared beforehand for the central thoughts of the 01-igin. To the new teaching all the naturalist side of his nature re­sponded, but from it the religious side recoiled. R eligion conquered in the strife, but the natural-

' In Father a"cl Son, Lonclon, 1907.

16 FIFTY YEARS OF DARWINISM

ist found comfort in the perfectly logical con­clusion that:-

" Any breach in the circular course of nature could be conceived only on the supposition that the object created bore false witness to past processes, which had never taken place." 1

Thus the divergence between the literal inter­pretation of Scripture and the conclusions of both geologist and evolutionist ,vere for this re­markable man reconciled by the conviction:-

" T hat there had been no gradual modification of the surface of the earth, or slow development of organic forms, but that when the catastrophic act of creation took place, the world presented, instantly, the structural appearance of a planet on which life had long existed." 2

Philip Gosse could not but belie,1e that the thoughts which had brought so much comfort to himself would prove a blessing to others also. H e offered Omphalos '' with a glowing gesture, to atheists and Christians alike. . . . But, alas I atheists and Christians alike looked at it and laughed, and threw it away." s Charles l{ingsley expressed the objection felt by the Christian ·when he ,vrote that he could not " be­lieve that God had ,vritten on the rock one enor­mous and superfluous lie."•

About twenty yea.rs ago I ,vas present ,vhen precisely the same conclusion was advanced by a high dignitary of the English Chw·ch. H e argued that even if the history of the Universe

• Father an,d, Son, pp. lf20, H!l. • L . c., p. lf22.

' L. c., p. 120. • Ibid.

FIFTY YEARS OF DARvVINISM 17

,vere carried back to a single element such as hydrogen, the human nund ,vould remain unsat­isfied and would inquire ,vhence the hydrogen came, and that any and every underlying form of matter must leave the inexorable question " ,vhence?" still unanswel'ed. Therefore if in the end the question must be given up, we may as ,vell, he argued, admit the mystery of creation in the later stages as in the earlier. T hus he arrived at the belief in a world formed instanta­neously, ready-made and complete, with its f os­sils, marks of denudation, and evidences of evolu­tion-a going concern. Aubrey Moore, the clergyman who more than any other man was responsible for breaking down the antagonism tO'ward evolution then ,videly felt in the English Church, replied very much as Kingsley had done, that he was unwilling to believe that the Creator had deliberately cheated the intellectual po,vers H e had made. I may add that, inasmuch as science consists in the attempt to carry down causation as far as possible, it is above all the scientific side of the human intellect that is out­raged,-no weaker term can be used,-by this more modern development of the argument of Omphalos.

THE PUBLICATION OF THE DARWIN­WALLACE ESSAY

I n May, 1856, D arwin, urged by L yell, began to prepare for publication. He had determined

18 FIFTY YEARS OF DARWINISi\i

to present his conclusions in a volume, for he was unwilling to place any responsibility for his opinions on the council of a scientific society. On this point he was, as he told Sir Joseph Hooker, in the only fit state for asking advi,ce; namely, ,vith his mind firmly made up: then good advice was very comforting while it ,vas perfectly easy to reject bad advice. The work was continued steadily until June 18, 1858, when Wallace's let­ter and essay arrived from Ternate. As a result of the anniversary held in London on July 1 last year new light has been thrown upon the circum­stances under which the joint essay was published fifty years before.

In consequence of the death of the eminent botanist, Robert Brown, Vice-President and ex­President of the Linnean Society, the last meet­ing of the summer session, called for June 17, was adjourned. The by-laws required that the vacancy on the Council should be filled up with.in three months, and a special meeting was called for July 1, for this purpose. Darwin received Wallace's essay on June 18, too late for the sun1-mer meetings of the Society, but in good time for Lyell and Hooker to present it to the special meeting. Hence, as Sir Joseph Hooker said on July 1st last, the death of Robert Brown caused the theory of Natural Selection to be " given to the world at least four months earlier than ,vould otherwise have been the case." Sir Joseph Hooker also informed . us that from June 18 up

FIFTY YEARS OF DARWINISM 19

to the evening of July 1, ,vhen he met Sir Charles Lyell at the Society, all the intercourse with Dar,vin and with each other ,vas conducted by letter, and that no fourth person was admitted into their confidence. The joint essay ,vas read by the secretary of the Society. D a1·win ·was not present, but both L yell and H ooker " said a fe,v ,vords to emphasize the importance of the subject." Among those who ·were present ,vere Oliver, Fitton, Carpenter, Henfrey, Burchell, and B entham, ,vho ,vas elected on the Council and nominated as Vice-President in place of R obert Brown. I cannot resist the t emptation to reprint from the memorial volume issued by the Linnean Society of London some passages in the address which A. R. Wallace felt con­strained to deliver on J uly 1, 1908, protesting against the too great credit which he believed had been assigned to himself. After describing Dar­·win's discovery of Natural Selection and the t,venty years devoted to confirmation and patient 1·esearch, Wallace continued:-

" I-low different from this long study and preparation -this philosophic caution-this determination not to make known his fruitful conception till he could back il up by overwhelming proofs-was my own conduct. The idea came to me, as it had come to Darwin, in a sudden ·flash of insight: it was thought out in a few hours­was written down with such a sketch of its various appli­cations and developments as occurred to me at the moment,-then copied on thin letter-paper and sent off to Darwin-all within one week. I was then ( as often since) the ' young man in a hurry '; he, the painstaking

~0 FIFTY YEAR S OF DARWINISM

and patient student, seeking ever the full demonstration of the trutlh he had discovered, rather than to achieve immediate personal fame.

" Such being the actual facts of the case, I should have had no cause for complaint if the respective shares of Darwin and myself in regard to the elucidation of nature's method of organic development, had been thenceforth estimated as being, roughly, proportional to the time we had each besitowed upon it when it was thus first given to the world-that is to sa.y, as twenty years is to one week. For, he had already made it his own. I f the persuasion of his friends had pl"evailed with him, and he had published his theory after ten years', fifteen years', or even eighteen years' elaboration of it, I should have had no part in it whatever, and he would have been at once recognized, and should be ever recog­nized, as the sole and undisputed discoverer and patient investigator of the great law of 'Natural Selection' in all its far-reaching consequences.

"It was really a singular piece of good luck that gave me any share whatever in the discovery . . . it was only D arwin's extreme desire to perfect his work that allowed me to come in, as a very bad second, in the truly Olympian race in which all philosophical biologists, from Buff on and Erasmus Darwin to Richard Owen and Robert Chambers were more or less actively engaged."

ECHOES OF THE STORM

I t is impossible to do n1ore than refer briefly to the storm of opposition \vith ,vhich the Origin was at first received. The revie,ver in the Athe­nr,eu1n for November 19, 1859, left the author " to the mercies of the D ivinity I-Iall, the Col­lege, the Lecture Roon1, and the Museum." 1

Dr. , ¥hewell for some years refused to allow a • Life a11d Letters, II, p. !1!18 n.

F IFTY YEARS OF DARvVINISM ~l

copy of the Origin to be placed in the library of T rinity College, Cambridge.1 l\!Iy predecessor, P rofessor J. 0. vVestwood, proposed to the last Oxford University Commission the permanent endo,vment of a Reader to combat the errors of D ar,vinism. " L yell had difficulty in preventing [Sir vVilliam] D a,vson revie,ving the Origin on hearsay, ,vii.thout having looked at it. No spirit of fairness can be expected from so biased a judge." 2 And even ,vhen naturalists began to be shaken by the force of D ar,vin's reasoning, they \Vere of ten afraid to own it. Thus D ar,vin ,vrote to H . F a,vcett, on September 18, 1861 :-

" i\Iany are so fearful of speaking out. A German naturalist came here the other day; and he tells me that there are many in Germany on our side, but that all seem fearful of speaking out, and waiting for some one to speak, and then many will follow. The naturalists seem as timid as young ladies should be, about their scientific reputation." 3

Among the commonest criticisms in the early days, and one that Darwin felt acutely,• ,vas the assertion that he had deserted the true method of scientific investigation. One of the best exam­ples of these is to be found in the letter, D ecem­ber 24, 1859, of D arwin's old teacher in geology, A dam Sedg,vick :-

' Life and Letters, II, p. 261. • From a letter written by Darwin, November 4, 1862. Mo,·e

L etters, I, p . 468. • JJ1ore Letten, I, p . 196. • See Darwin's letter to Henslow, May 8, 1860. More Letters,

I, pp. 149, 150.

2~ FIFTY YEARS OF DARWINISM

"You have deserted-after a start in that tram-road of all solid physical truth-the true method of induc­tion, and started us in machinery as wild, I think, as Bishop Wilkins's locomotive that was to sail with us to the moon." 1

These ,~,ild criticisms were soon set to rest by H enry Fawcett's article in Macmillan's M aga­zine in 1860 and by a paper read before the British Association by the same author in 1861. Referring to this defense, Fawcett wrote to D ar­·win, J uly 16, 1861:-

" I was particularly anxious to point out that the method of investigation was in every respect philosoph­ically correct. I was spending an evening last week with our friend ~1r. John Stuart ~1ill, and I am sure you will be pleased to hear that he considers your reason­ing throughout is in the most exact accordance with the strict principles of logic. He also says the method on investigation you have followed is the only proper one to such a subject. I t is easy for an antagonistic reviewer, when he finds it difficult to answer your argu­ments, to attempt to dispose of the whole matter by uttering some such commonplace as ' This is not a Baconian induction.' "

"As far as I am personally concerned, I am sure I ought to be grateful to you, for since my accident nothing has given me so much pleasure as the perusal of your bcok. Such studies are now a great resource to me." 2

• Life and Letter.t, II, p. !?+S. See also the Quarterly Review for July, lSGO. Sedgwick's review in the S pecl<ito1·, Match !l!, 1860, contains the following passage: " . . . I cannot conclude without expressing my detestation of the theory, becau~e of _its unflinching materialism; becau,e it has deserted the 111clucllve track, the on ly track ' that leads to physical truth; because it utterly repudiates final causes, and thereby indicates a demoralized understanding on the part of its advocates." (~noted in Life and Letters, ll, p . 298.

• Mo,·e L otte,·s, I, pp. 169, 190.

FIFTY YEARS OF DARWINISM ~8

T o this D ar,vin replied:-

" You could not possibly have told me anything which would have given me more satisfaction than what you say about l\>Ir. lVIill's opinion. Until your review appeared I began to think that perhaps I did not under­stand at all how to reason scientifically." 1

THE ~IATURITY OF THE ORIGIN CONTRASTED ,vITH THE CRUDITY OF RIVAL INTERPRE­TATIONS

It is remarkable to contrast the maturity, the balance, the judgment, ·with which Darwin put f or"vard his views, with the rash and haphazard objections and rival suggestions advanced by his critics. It is doubtful whethe1· so striking a con­trast is to be found in the history of science;­on the one side twenty years of thought and in­vestigation pursued by the greatest of naturalists, on the other offhand impressions upon a most con1plex problem hastily studied and usually very imperfectly understood. I t is not to be won­dered at that Dar"vin found the early criticisms so entirely ,vo1-thless. The following extract from an interesting letter 2 to John Scott, written on D ecember 3, 1862, shows how ,veil a,val'e he ,vas of difficulties unnoticed by critics:-

" You speak of difficulties on Natural Selection: there arc indeed plenty; if ever you J1ave spare time (which is not likely, as I am sure you mus t be a hard worker) I should be very glad to hear difficulties from one who has observed so much as you have. The major-

• More Letters, I, p. 189. ' iJl orc Letters, II, p. 311.

~4 FI FTY YEARS OF DARWINIS1V1

ity of criticisms on the Origin are, in my opinion, not worth the paper they are printed on."

From the very first the most extraordinarily crude and ill-considered suggestions were put for­\vard by those " 'ho ,vere unable to recognize the value of the theory of Natural Selection. A good example is to be found in Andre,v Mur­ray's principle of a sexual selection based on con­trast,-" the effort of nature to preserve the typ­ical medium of the race." ' And even in these later yea1·s the v,ildest imaginings may be put f Or\.vard in all seriousness as the interpretation of the ·world of living organisms. Thus in Beccari's interesting ,vork on Borneo,2 the author com­pares the infancy and gro"vth of the organic ,vorld ·with the development and education of an indi­vidual. In youth the individual learns easily, being unimpeded by the force of habits, ,vlrile " ,vith age heredity acts 1nore strongly, instincts prevail, and adaptation to ne,v conditions of ex­istence and to ne,v ideas becomes n1ore difficult; in a word, it is much less easy to combat hered­itary tendencies." Similarly in the state of ma­turity no,v reached by the organic ,vorld Beccari believes that the po,ver of adaptation is ,vell-nigh non-existent. Heredity, through long accumula­tion in the course of endless generations, has be­come so po,verf ul that species are 110,v stereo­typed and cannot undergo advantageous changes.

'Life and Letters, II, p. !'!61. • Wanderings in the O,·eat Forests of Borneo, London, 1904..

English translation, pp. 209-16.

FIFTY YEARS OF DARWINISM 25

F or the san1e reason acquired characters cannot no,v be transmiitted to offspring. Beccari imag­ines that everything ,vas different in early ages ,vhen, as he sup.poses, life ,vas young and heredity ,veak. I n this assumed " Plasmatic Epoch" the environment acted strongly upon organisms, evoking the responsive changes ·which have no,v been rendered iixed and inunovable by heredity.

E ven the hypothesis proposed as a substitute for Natural Selection by so distinguished a bot­anist as Carl Nageli turns out to be most unsat­isfactory the moment it is exa1nined. The idea of evolution under the compulsion of an internal force residing in the idioplasm is in essence but little removed from special creation. On the sub­ject of Nageli's criticisms D arwin ·wrote,1 Au­gust 10, 1869, to Lord Farrer:-

" It is to me delightful to see what appears a mere morphological character found to be of use. I t p leases me the more as Carl Niigeli has lately been pitching into me on this head. Hooker, with whom I discussed the subject, maintained that uses would be found for lots more structures, and cheered me by throwing my own orchids into my teeth."

DARWIN'S GREATEST FRIENDS IN THE TI~IE OF STRESS

I t is interesting to put side by side passages from t,vo letters 2 written by Dar,vin to H ooker, one in 1845 at the beginning of their friendship,

''!>fore Letters, II, p. SSO. • L. c., I, p. $9. The passages here quoted are put side by side

by the editors of this work.

~6 FIFTY YEARS OF DARWINIS?II

the other thirty-six years later, a few months be­fore Darwin's death. The first shows the instant growth of their friendship: "Farewell! What a good thing is community of tastes! I feel as if I had known you for fifty years. Adios."

The second letter expresses at the end of Dar­win's life the same feelings which find utterance ever and again throughout the long years of his friendship.

" Your letter has cheered me, and the world does not look a quarter so black this morning as it did when I wrote before. Your friendly words are worth their weight in gold."

The friendship with Asa. Gray began with a n1eeting at I(e,v some years before the publica­tion of Natural Selection. Darwin soon began to ask for help in the ,vork, which ,vas ultimately to appear as the Origin. The following letter to Hooker, J une 10, 1855, shows what he thought of the great American botanist:-

" I have written him a very long letter, telling him some of the points about which I should feel curious. But on my life it is sublimely ridiculous, my making suggestions to such a man." 1

The friendship ripened very quickly, so that on July 20, 1856, Darwin gave Asa Gray an account of his views on evolution/ and on Septe1nber 5

of the following year a tolerably full description 3

' .,t o•·e Letters, I, p. 418. Asa Gray's generous reply is printed on p. 421.

' Life and, Letters, II, p. 78. • L. c., pp. 119, 120.

FIFTY YEARS OF DARWINIS1I 27

of Natural Selection. From this latter letter Dar,vin chose the extracts ,vhich forn1ed pa.rt of his section of the joint essay published J uJy 1, 1858.

Asa Gray's opinion on first reading the Origin "'as expressed not to Darwin. but to Hooker in a letter ,vritten January 5, 1860 :-

" I t is done in a 1nasterLy 1nanner. It might well have taken twenty years to produce it. I t is crammed full of most interesting matter-thoroughly digested­well expressed-close, cogent, and taken as a system it makes out a. betlter case than I had supposed pos-"bl " SI e. . . .

After attending to Agassiz's unf avorable opinion of his book, he continues: " Tell D arwin all this. I ,vill ,vrite to hi1n ·when I get a chance. As I have promised, he and you shall have fair play here. . . . " 1 A little l ater, ,vhen on Jan­uary 23, he wrote to D arwin himself, Asa Gray concluded: " I am free to say that I never learnt so much from one book as I have from yours." 2

It is impossible to do justice on the present occasion to the numerous lettel's in ,vhich Dar,vin expressed his g1·atitude for the splendid manner in ·which Asa Gray kept his ,vord and " fought like a hero in defense." 3 At a time ,vhen fevr naturalists were able to understand the driif t of Dar,vin's argument, the acute and penetrating mind of A.sa Gray had in a moment mastered every detail. Thus Darwin wrote on July 22,

' Life ancl Letter8, II, p. 268. • L. c., p. 27!!. • L. c., p. $10.

~8 FIFTY YEARS OF DARWI NISl\'1

1860, concerning the article in the Proceedings of the American Academy for April 10 :-

" I can not resist expressing my sincere admiration of your most clear powers of reasoning. As Hooker lately said in a note to me, you are more than any one else the thorough master of the subject. I declare that you know my book as well as I do myself; and bring to the question new lines of illustration and argument in a manner which excites my astonishment and almost my envy ! . . . Every singUe word seems weighed carefully, and tells like a 3~-pound shot." 1

Some ,veeks later, on September 26, 1860, D arwin again expressed the same admiration, and stated that Asa Gray understood him more perfectly than any other friend:-

" . .. You never touch the subj ect wjthout making it clearer. I look at it as even more extraordinary that you never say a word 01· use an epithet which docs not express fully my meaning. Now L yel1, Hooker, and others, who perfectly understand n1y book, yet sometimes use expressions to which I demur." •

D arwin also sent 3 Asa Gray's defense of the Origin to Sir Charles L:irell, ·whom he ,vas ex­tremely anxious to convince of the truth of evolu­tion. Asa Gray's religious convictions pre­vented the full acceptance of Natural Selection. H e ,vas ever inclined to believe in the Providen­tial guidance of the strea1n of variation. He also differed from D arwin in the interpretation of all instincts as congenital habits.•

• Li/ e a"d Lotte,·s, II, p. 3!!6. ' L. c., pp. 344, 345. • illore Letters, I, p. 169. • Life an<l Letters, III, p. 170.

FIFTY YEARS OF DARWINIS:M: ~9

The same close intimacy and mutual he]p be­gun in the preparation of the Origin was con­tinued in Dar,vin's later botanical ,vorks. Thus Dar,vin o,\·ed his Climbing Plants to the study of a paper by Asa Gray, and he dedicated his Forms of Flotr;ers to the American botanist " as a small tribute of respect and affection." Concerning some of the researches ,vhich after­,vard appeared in this book, Dar,vin wrote: 1

" I care more for your and Hooker's opinion than that of all the rest of the world, and for L yell's on geological points."

Another great name, that of Huxley, is espe­cially associated in our minds with the defeat of those who ,vould have denied that the subject was a proper one for scientific investigation. In the strenuous and memorable years that followed the appearance of the Origin the mighty warrior stands out as the man to whom more than to any other ,ve o,ve the gift of free speech and free opinion in science,-the man so admirably de­scribed by Sir Ray Lankester at the Linnean celebration, " the great and beloved teache1·, the unequaled orator, the brilliant essayist, the un­conquerable champion and literary s,vordsman­Thomas Henry Huxley."

Comparing the friendships to which Darwin o,ved so much, Lyell ,vas at first the teacher but finally the pupil,-un,villing and unconvinced at the outset, in the end convinced although still

' Life a11d Letters, III, p. 300.

SO FIFTY YEARS OF DARWINISlVI

unwilling; Hooker in England and Asa Gray in America ,vere the two intimate friends on ·whom he chiefly depended for help in writing the Origin and for supports to its arguments; Huxley ,vas the great general in the field ·where religious con­victions, expressed or unexpressed, ,vere the foundation of a fierce and bitter antagonism.

THE ATTACKS OF RICHARD O'\-VEN AND ST. GEORGE !IIIVART

An unnecessary bitterness ·was irnported into the early controversies in England, because of the personality of the scientific leaders in the attacks on the 01-igin. Of these the chief ,vas the great con1parative anatomist, Richard O,ven. In spite of his leading scientific position, this re­markable man withdrew from contact with his brother zoologists, living in a self-imposed isola­tion which tended towards envy and bitterness. The same unavailing detachment had been car­ried mucl1 further by the great naturalist W. J. Burchell, ,vho, as from a ,vatch-to,ver, looked upon the ,vorld he strove to aYoid ,vith an ab­sorbed and jealous interest. Professor J. l\f. Bald,vin has sho,vn how inevitable and inexorable is the grip of the social environment: the more we attempt to evade it the more firrnly ·we seem to be held in its grasp.

In the first yeru:s of the struggle O,ven's bitter antagonism made itself felt in the part he took as " crammer " to the Bishop of Oxford, and in

FIFTY YEARS OF DARWINISM 31

his anonyrnous article in the Edinburgh Review for April, 1860. But O·wen could not bear to remain apart f ron1 the stream of thought when there was no doubt about the ,vay it was flo·wing, so that in a few years he was maintaining son1e of the chief conclusions of tlhe Origin, although retracting nothing, but rather keeping up his bit­ter attacks upon Darwin. This treatment re­ceived from one who was all affability 1 ,vhen they met ,vas natu1·ally resented by Dar,vin, whose

·feelings on the subject are expressed in the fol­lo·wing passage from a letter to Asa Gray, z July 23, 1862:-

"By the way, one of my chief enemies ( the sole one who has annoyed me), namely Owen, I hear has been lecturing on birds; and admits that all have descended from one, and advances as his own idea that the oceanic wingless birds have lost their wings by gradual disuse. He never alludes to me, or only with bitter snee1·s, and coupled with Bulfon and the Vestiges."

In the historical sketch added to the later edi­tions of the Origin, O,ven is the only writer ,\1ho is severely dealt with. In this introductory sec­tion Darwin said that he was unable to decide whether Owen did or did not claim to have orig­inated the theory of Natural Selection.3

About twelve years after the appearance of the Origin another opponent, St. George Mivart,

•"Mrs. Carlyle said that Owen's sweetness always reminded her of sugar of lead." Life and Letters of T. H. Huxley, London, If, p. 167.

• i\Io-re Letters, I, p. 903. • Origin of Svecie.s, 6th ed., p. xviii.

Si FIFTY YEARS OF DAR,VINISM

produced something of' the same bitterness as Owen and for a similar reason. Thus D ar,vin wrote 1 to H ooker, September 16, 1871, as fol­lows:-

" You never read such strong letters lVIivart wrote to me about respect towards me, begging that I would call on him, etc., etc.; yet in the Q. Revur<i.l [July, 1871] he shows ithe greatest scorn and animosity towards me, and with uncommon cleverness says all that is most disagreeable. He makes me the most arrogant, odious beast that ever lived. I ,can not understand him; I suppose that accursed religious bigotry is at the root of it. Of course he is quite at liberty to scorn and hate me, but why take such trouble to express something more than friendship? I t has mortified me a good deal."

On other occasions at a much later date I have myself observed that there ,vas something pecu­liar about the poise of ~Iivart's mind, which seemed ever inclined to pass ,vith abrupt transi­tion from the extreme of an unnecessary effusive­ness to an unnecessarily extreme antagonism.

Mivart's attack, contained in his book The Genesis of Species, was effectively dealt ,vith by Chauncey Wright in the North A 1nerican Review for July, 1871. Dar,vin ,vas so pleased ,vith this defense that he obtained the author's permission for an English reprint,2 and ,vith fur­ther additions it ,vas published as a pamphlet by

' More Letters, I, p. 333. See also Li/ e and Lettei·s, Ill, p. 147. . . . .

' The pamphlet was published at Darwin s e~pense. For his keenly app reciative Jetter to the author sec L1f.e and Letters, III, p. 145.

FIFTY YEARS OF DARWINISM SS

John l\l[urray in 1871. A copy presented by Dar·win to the late J. Jenner Weir and now in the Library of the H ope D epartment of Oxford University ~Iuseum contains an interesting holo­graph letter ref erring to the pamphlet and bear­ing upon the controversy that follo,ved upon the appearance oi lVl ivart's book. This letter is, by kind permission of the D arwin family, now made public:-

"Down, " Beckenham, Kent.

" Oct. 11, 1871. " My dear Sir

" I am much obliged for your kind note & invitation. I shd like exceedingly to accept it, but it is impossible. I have been for some months worse than usual, & can withstand no exertion or excitement of any kind, & in consequence have not been able to see anyone or go anywhere.-As long as I remain quite quiet, I can do some work, & I am now preparing a new and cheap Editn of the Origin in which I shall answer Mr. l\llivart's chief objections. Huxley will bring out a splendid review on d0 in the Conte1nporary R., on November 1st.

"I am pleased that you like Ch. \Vright's article. It seemed to me very clever for a man who is not a naturalist. He is highly esteemed in the U. States as a JVIathematician & sound reasoner.

"I wish I could join your party.­" i.VI y dear Sir

" Yours very sincerely " CH. D ARWIN." l

Chauncey , ¥right speaks of presenting, in his 1·evie,v of lV[ivart, considerations " in def ense and

1 The letter is addressed to J. Jenner ,veir, Esq., G Haddo Villas, Blackheath, London, S. E.

34 FIFTY YEARS OF DARWINISM

illustration of the theory of Natural Selection. My special purpose," he continues, "has been to contribute to the theory by placing it in its proper relations to philosophical inquiries in general." 1

This able critic in Ainerica and Henry Fa,vcett in En.gland represent a class of thinkers ,vho have taken and still take a very important part in up­holding the theory of J\T atural Selection. It is not necessary to be a biologist in order to compre­hend the details and the bearings of this theory. They were at the very first understood by able thinkers ,vho were not scientific men or who fol­lowed some non-biological science, when natural­ists themselves ,vere hopelessly puzzled. And at the present time such support is of the highest importance when ,vithin the limits of the sciences most nearly concerned the intense and natural desire to try all things is not ahvays accompanied by the steadfast purpose to hold fast that '\\•hich is good.

LAl\>fARCK'S HYPOTHESIS AND THE HERED­ITARY TRANS:'IIISSION OF ACQUIRED CHAR­ACTE RS

The greatest change in evolutionary thought since the publication of the Origin was ,vrought, after Dar,vin's death, by the appearance of that wonderful and beautiful theory of heredity, which looks on parents as the elder brother and sister of their children. In this theory, itself an outcome of minute and exact observation,

• Life and Lettei·s, III, pp. 143, 14-!.

FIFTY YEARS OF D.ARvVINISNl 85

W eismann raised the question of the hereditary transmission of acquired characters, the very foundation of La1narckian evolution. D ar,vin accepted such transmission, and it ,vas in order to account for " the inherited effects of use and disuse, &c.," 1 that he thought out his 1narvelous hypothesis of pangenesis. I f such effects be not t ransmitted pangenesis becomes unnecessary and W eismann's simpler, more convincing, and bet­t er supported hypothesis of the continuity of the germ-plasm takes its place. It is iinpossible on the present occasion to speak in any detail of the controversy ,vhich has raged intermittently dur­ing the past t,venty years on this fascinating sub­ject. I ,vill, ho,vever, briefly consider a single example of the error into vvhich, as I believe, D ar,vin ,vas led by f ollo,ving the Lamarckian theory of hereditary experience. I refer to the interpretation ,vhich he suggests for feelings of " the sublime," applying this te11n to the effect upon the brain of a vast cathedral, a tropical for­est, or a vie,v from a mountain height. ·T hus, writing to E. Gurney, J uly 8, 1876, Dar,vi111 said on this subject :-". . . possibly the sense of sublimity excited by a grand cathedral n1ay have some connection ,vith the vague feelings of terror and superstition in our savage ancestors, ,vhen t hey entered a great cavern or gloo1ny forest." 2

An interesting account is given by Romanes 3

1 See the letter to Huxley, July H! (1865?), in Life and Lettel's. • Life and L etters, III, p. 186. • Ib,d., pp. 54, 55. See also I, pp. 64-, 65.

36 FIFTY YEARS OF DARWINISM

of Darwin;s o,vn experiences of this feeling, re­lating ho,v he at first thought that they w·ere most excited by the magnificent prospects surveyed from the summits of the Cordilleras, but after­wards came do,vn from his bed on purpose to correct this impression, saying that he felt most of the sublime in the forests of Brazil.

We may first observe that the remarkable feel­ings induced by such experiences are very far from unpleasant, as we should expect them to be on the theory which refe1·s them to the apprehen­sions and dangers of our primitive ancestors. Thus, on J\1ay 18, 1832, when the first irnpres­sions of a Brazilian forest were freshest in Dar­,vin's mind, he ,vrote to H enslow, telling him of an expedit ion of 150 miles from Rio de J aneiro to the R. I\1acao.

" Here I first saw a tropical forest in all its sublime grandeur-nothing but the realjty can give any idea how wonderful, how magnificent the scene is. . . . I never experienced such intense delight. I formerly admired Humboldt, I now almost adore him; he alone gives any notion of the feelings which a.re raised in my mind on first entering the tropics." '

Furthermore, how are we to account on any such hypothesis for the similarity of the feelings excited by the forest, ,,rhere enenues might lurk unseen, and the mountain peak, the very spot " 'hich offers the best facility for seeing them? I t is also difficult to understand ,vhy the terrors of primitive man should be specially associated ,vith

• Lifo a1ul Lott.ors, I, pp. ~6, f.?37.

FIFTY YEARS OF DARvVINIS~f 37

ca?es or ,vith the most magnificent forests on the face of the earth. There is 1110 valid reason for believing that any less danger lurked anlid trees of ordinary size or lay in ·wait for him by the riverside, in the jungle, or the rock-stre,vn waste. In the midst of life he ,vas in death in every sol­itary place that could afford cover to an enemy; on the mountain top probably least of all.

The feelings inspired by the interior of a cathe­dral are especially instructive in seeking the ex­planation of the psychological effect. ,;v e may be sure that the brain effect is here produced by the unaccustomed scale of the esthetic impression. A cathedral the size of an ordinary church would not produce it. H owever intensely we may ad­mire, the sense of the sublime is not excited or but feebly excited by the exterior of a cathedral, nor does it accompany the profound intellectual interest aroused by the sight of the pyramids. The thrill of the sublime, in the sense in which the tern1 is here used, is, I do not doubt, the result of surprise and ,vonder raised to their highest power -a psychological shock at the reception of an esthetic visual experience on an unwonted scale, -vast as if belonging to a larger world in which the insignificance of man is forced upon him. It is not excited by the pyramids which are in form but symmetrical hills of stone, nor does the ex­terior of any building afford an experience suf­ficiently remote to produce the feeling in any high degree.

38 FIFTY YEARS OF DARWINISNl

W. :J. :Burchell, in one of his letters 1 to Sir , villiam H ooker, points out that the feelings of a,ve and wonder aroused in a Brazilian forest are not to be expected in those to ,vhom the sight is

. familiar. As regards the depth and nature of the effects produced by the experiences here re­f erred to, it ,vould be very interesting to com­pare the savage with the civilized man, the uned­ucated ·with the educated mind. That the results are intimately bow1d up with the psychological differences between individuals-in pa1-t inherent, in part due to training and experience-is well illustrated in a story told by the late Charles Dudley , ;y arner, who took t,vo English f riencls to see for the first time the Grand Canyon of the Colorado. V\Then they reached the point where the ,vhole prospect-boundless beyond im­agination-is revealed in a moment of time, one of his friends burst into tears, ,vbile the other relieved his feelings by unbridled blasphemy. · The remarkable psychological effects of a grandeur far transcending and far removed from ordinary experience may be co1npared to the thrill 2 so often felt on hearing majestic music, a thrill ,ve do not seek to explain as a faint, far-off reminiscence of dread inspired by the savage war­cry. I do not doubt that an explanation of the sublime based on the ter rors of our pri1nitive an-

, Preserved in the Libra1·y at Kew, but, I belie,•e, as yet unpub­lished.

' Darwin spoke of bis backbone shivering cluri!llg the anthem in King's College chapel. Life 11111! Letters, I, p. 49; see also p. 170.

FIFTY YEARS OF DARWINISl\1 39

cestors is an example of the mistaken interpre­tations into ,vhich even Dar,vin ,vas led by fol­lo·wing the hypothesis of Lamarck.

FRANCIS DARWIN ON THE TRAKSJ.IISSION OF ACQUIRED CHARACTERS

One of the most recent attempts to de£ end! the Lamarch.-ian doctrine of the hereditary transmis­sion of acquired characters is contained in the important Presidential Address of Mr. Francis D ar,vin to the British Association at Dublin (1908). In this interesting memoir the author expresses his belief that such transmission is im­plied by the persistence of the successive develop­mental stages through ,vhich the individual advances to,vard maturity. Follo,ving H ering and Richard Semon he is disposed to explain the hereditary transmission of these stages by a process analogous to memory. It is interesting to observe that this very analogy had been brought before Charles Dar"1in, but failed to sat­isfy him. He wi-ote 1 to G. J. R o1nanes, lVIay 29, 1876:-

• More Letters, I, p . 364. See also the following sentence in a letter on Pangenesis, written June 3, 1868, to Fritz Millier: "It often appears to me almost certain that the characters of the parents are 'photographed ' on the child, only by mea.ns of material atoms derived from each cell in both parents, and devel­ope<l in the child." M o1'e Letters, II, p . 5g_ The following passage in a letter to Sir Joseph Hooker, February 28, 1868, is also of great interest: "When you or Huxley say that a single

· cell of a plant, or the stump of an amputated limb, has the 'potentiality• of reproducing the whole or 'diffuse an inHuence,' these words gh·e me no positi~e i'clea ;-but when it is sa.id that the. cells of a plant, or stump, include a.toms derived from every other cell of the whole organism and capable of development, l gain a distinct idea." Life and Letters, III, p. 81.

40 F IFTY YEARS OF DARWINISM

" I send by this post an essay by Hackel attacking Pan. and substituting a. molecular hypothesis. If I understand his views rightly, he would say that with a bird which strengthened its wings by use, the forma­tive protoplasm of the strengthened parts became changed, and its molecular vibrations consequently changed, and that these vibrations are transmitted throughout the whole frame of the bird, and affect the sexual elements in such a manner that the wings of the offspring are developed in a like strengthened manner. . . . He lays much stress on inheritance being a form of unconscious memory, but how far this is a parfl; of his molecular vibration, I do not under­stand. His views make nothing clearer to me; but this may be my fault."

Should it hereafter be proved that acquired characters are transmitted, I can not but think that the interpretation ,vill be on the lines of Charles Dar,vin's hypothesis of Pangenesis. But the probability that any such result ,vill be estab­lished, already shown to be extremely small, has become even more ren1ote in the light of the re­cent investigations conducted by l\1endelians and mutationists.

For the transmission of all inherent qualities, including the successive stages of individual de­velopment, '\i\T eismann's hypothesis of the con­tinuity of the germ-plasm supplies a sufficient mechanism. I remember, more than twenty years ago, asking this distinguished discoverer how it was that the hypothesis arose in his mind. He replied that "'hen he ,vas working upon the germ-cells of Hydrozoa he realized that he ,vas dealing ,vith material which was most carefully

FIFTY YE.'\RS OF DARWINISM 41

preserved as if of the most essential importance for the species. If the efficient cause of the stages of ontogeny resides in the fertilized ovum -as ,ve cannot doubt-,v eisrnann's hypothesis satisfactorily accounts for their hereditary trans­nuss1on. For the portion of the ovum set aside to form the germ-cells from ,vhich the next gen­eration will arise is reserved with all its powers and includes the potentiality of these stages no less than the other inherent characteristics of the individual.

I t is, I think, unfortunate to seek for analogies -and vague analogies they must ah,vays be­between heredity and memory. However much we have still to learn about it, memory is, in its physiological side, a definite property of certain higher cerebral tissues,-a property which has clearly been of the utmost advantage in the strug­gle for life and bears the stamp of adaptation. Compare, for instance, the difficulty in remem­bering a name with the facility in recognizing a face. A daptation ,vottld appear to be even more clearly displayed in the unconscious registration in memory and the instant recognition of another individual as seen from behind or ,vhen partially concealed. Such memory is quite independent of the artistic po"rer. Without any intelligent appreciation of what is peculiar to another indi­vidual, his characteristic features are stored up unconsciously so that ,vhen seen again he is in­stantly recognized.

4~ FIFTY YEARS OF DARWINIS!\'1

One other consideration brought forward by Mr. Francis Dar,vin may be briefly discussed. It is well known that plants have the power of adjusting themselves to their individual environ­ment, and that such adjustment may beneficially take the place of a rigid specialization. The static condition of plants renders this power e,spe­cially necessary for them, and the hereditary transmission of the results of its exercise espe­cially dangerous. Where the seed falls, there must the plant grow. The parent .vas limited to one out of many possible environments; the off­spring may grow in any of them, and for one that would hit off the precise conditions of the parent and would benefit by inheriting the parental response, numbers would have to live in different surroundings and might be injured by the hereditary bias.

lV[r. Francis Darwin calls attention to the leaves of the beech, which in the interior, shaded parts of the tree possess a structure different from that exhibited in the outer parts more freely

· exposed to light. The structure of the shaded leaves resembles that apparently stereotyped in trees permanently aidapted to shade, and iir. Francis Dar~vin is inclined to regard the fixed condition as a final result of the hereditary trans­mission of the same response through a large number of generations.

The development of shade foliage in the beech is, I presume, a manifestation of a po,ver ,videly

FIFTY YEARS OF DARWINISl\i 43

spread an1ong animals and probably among plants also, a po·wer of producing a definite individual adaptation in response to a definite stimulus. To stereotype the result ,vould be to convert a benefit to the individual into an injury to the species. The beech in a very shady place would presumably develop the maximum of the shade foliage. Ho,v disadvantageous would the hered­itary bias be to its offspring that happened to grow in more exposed situations. But, it is argued, in plants subject to the fixed condition ,ve do meet ,vith the fixed structure, just as if repetition had at length produced an hereditary result. The ans'l-ver to this argument seems to me to be complete. , vhen conditions are uni­form and no power of individual adaptation is 1·equiTed, Natural Selection, ,vithout attaining the power, would produce the :fixed result in the usnal '\\1ay. I f, ho'\\1ever, a species already pos­sessing the power, ultimately came to live perma­nently in one set of conditions and thus ceased to need it, the po'l-ver itself, no longer sustained by selection, '\\7ould sooner or later be lost.

DAR\VIN'S VIE'\>VS ON EVOLUTION BY " 1'IUT ATION "

I t is interesting to note that the term" Muta­tion "appears at one time to have suggested itself to D arwin 1 in order to express the evolution or

• This seems clear from the following passage in a letter written February 14-, 1845, to Rev. L . Blomefield (Jenyns): "Thanks for your hint about terms of 'mutation,' etc.; I had

44 FIFTY YEARS OF DARWINIS:VI

descent with 1nodification of species, by no means implying change by large and sudden steps as in the usual modern acceptation of the term. In­deed, the "vords "1nutable," " mutability," and their opposites have never been employed ,vith the special significance now attached to " muta­tion." Every one believes in the 1nutability of species, but opinions differ as to whether they change by mutation.

It is a mistake to suppose that Dar°l'vin did not long and carefully consider large variations, or " mutations," as supplying the material for evo­lution. Writing to Asa Gray as early as August 11, 1860, he sa.id 1 of great and sudden varia­ation :-

" I have, of course, no objection to this, indeed it would be a great a.id, but I did not allude to the subject, for, after n1uch labor, I could find nothing which satis­fied me of the probability of such occurrences. There seems to me in almost every case too much, too complex and too beautiful adaptation in every structure to believe in its sudden production."

In the t\\,enty years bet°l'veen 1860 and 1880 ,ve find that D arwin was continually brought back to this subject by his correspondents, and by re­viev,rs and criticisms of his \.York. Scattered over

some suspicions that it was not quite correct, and yet I do not yet see my way to arrive at any better terms. It ~VIII be ye~rs befoi·e I publish, so that T shall h,we plenty of tune_ to tl,~nk of better words. Development would perhaps do, only ,t applied to the changes of an individual during its growth." Mo,·e LeUers, I, p. 50.

• Life a11d Lette,·s, II, pp. 333, 33<k

FIFTY YEARS OF DARWINIS~1 45

this period \Ve find nun1bers of letters in ·which he expressed his disbelief in an evolution founded on " sudden jumps " or " monstrosities," as ~,ell as on " large," " extre1ne," and " great and sudden variations." Out of many examples I select one more because of its peculiar interest. The Duke of .Al'gyll had criticised Da.r\vin's theory of Nat­ural Selection as though it had been a theory of mutation, an interpretation repudiated by D arwin.

The Duke of Argyll in his address 1 to the R oyal Society of Edinburgh, D ecember 5, 1864, had said:-" Strictly speaking, therefore, Mr. Dar,vin's theory is not a theory of the Origin of Species at all, but only a theory on the causes which lead to the relative success and failure of such new forms as may be born into the ,vorld." In a letter to Lyell (January 22, 1865), Darwin ·wrote concerning this argument of the D uke's:-

" I demur . . . to the Duke's expression of ' new births.' That may be a very good theory, but it is not mine, unless he cal1s a bird born with a beak 1-l00th of an inch longer than usual ' a new birth'; but this is not the sense in which the term would usually be under­stood. The more I work the more I feel convinced it is by the accumulation of such extremely slight varia­tions that new species arise." 2

_ I desire again to state most emphatically that, during the whole course of his researches and re­flections upon evolution, D arwin was thoroughly

• Scotsma1t, December 6, 1864. 'Life and Letters, Ill, p. SS.

46 FIFTY YEARS OF DARWINIS"'11

aware of the ,videspread large variations upon which the mutationist relies. He had the mate­rial before him, he formed his judgment upon it, and on this memorable day it seems specially appropriate to show ho"v extraordinarily sure his scientific instincts were wont to be. This will be made clear by a f e,v exa1nples of the solution which Dar"vin found for problems ·which at the time had either not been attempted at all or had been very differently interpreted.

Dar\>vin's explanation of coral islands and atolls, at first generally accepted, ,vas after,vards called in question. Fina]ly, the conclusive test of a deep boring entirely confirmed the original theory. Perhaps the most remarkable case is that of the permanence of ocean basins and con­tinental areas, a view which D arwin maintained single-handed in Europe, although supported by Dana in America, against Lyell, Forbes, Wal­lace, Hooker, and all others who had ,vritten on the subject. D arwin considered it mere ·waste of time to speculate about the origin of life; we might as ,vell, he said, speculate about the origin of matter. Nothing hitherto discovered }1as shaken this opinion, which is expressed al­most in D arwin's words in Professor Arrhenius' recent work.1 In the fascinating subject of geo­graphical distribution we now know that Darwin anticipated Ed"vard Forbes in explaining the alpine arctic forms as relics of the glacial period,

• World$ in tlte Making. English translation, London, p. 190.

FIFTY YEARS OF DARWINISM 47

while he interpreted the pove1'ty of Greenland flora and the reappearance of north temperate spe,cies in the souithern part of South America as results of the same cause. Almost as soon as the facts were before hiin in W ollaston's memoirs, Darwin had inte1·preted the number of wingless beetles in oceanic islands as due to the special dangers of flight. He anticipated H. W. Bates' hypothesis of mimicry, but drove it from his mind because he did not feel confident about the geo­graphical coincidence of model and mimic. Long before the Origin appeared Darwin had thought over and rejected the idea that the same species could have more than a single origin or could arise independently in two different countries­a hypothesis very popular in later years, but, I believe, now entirely abandoned.

I should wish to advance one consideration be­fore concluding this section of my address. Cer­tain writers on mutation seem to hold the view that Natural Selection alone prevents large variations from of ten holding the field and leading to great and rapid changes of form. Such a view is not supported by the history of species which inhabit situations comparatively sheltered from the struggle, such as fresh water, caves, certain islands, or the depth of the ocean. Organisms in these places tend to preserve their ancestral structure more persistently than in the crowded areas ,vhere Natural Selection holds more potent sway.

48 FIFTY YEARS OF DARWINISN1

EVOLUTION CONTINUOUS OR DISCONTINUOUS

Dai·"vin fully recognized the limit to the results "''hich can be achieved by the artificial selection in one direction of individual variations. Thus he wrote,1 August 7, 1869, to Sir Joseph Hooker:-

"I am not at all surprised that Hallett has found some varieties of wheat could not be improved in cer­tain desirable qualities as quickly as at first. All expe1·ience shows this with animals; but it would, I think, be rash to assume, judging from actual experi­ence, that a little more improvement could not be got in the course of a century, and theoretically very improbable that after a few thousands [ of years'] rest there would not be a start in the san1e line of variation."

The conception of evolution hindered or for a time arrested for want of the appropriate varia­tions is far from new. The hypothesis of organic selection was framed by l3aldwin, Lloyd Mor­gan, and Osborn to meet this very difficulty, as expressed in the following paragraph quoted from the present writer's address to the Amer­ican Association for the Advancement of Science at the Detroit meeting, October 15, 1897 :-

" The contention here urged is that natural selection works upon the highest organisms in such a way that they have become modifiable, and that this power of pure]y individual adaptability in fact acts as the nurse by whose help the species . can live through

• More Letters, I, p. 314,.

F IFTY YEARS OF DARWINISl\i[ 49

times in which th~ needed inherent variations are not fo.rU1coming." 1

I t bas already been sho,vn that D ar,vin entirely recognized the limits which the variations now called " fluctuating " mey set to the progress achieved by artificial selectio:f:, a!1<l that he ad­mitted the necessity of ,vaiting for a fresh " start in the same line." In this respect he agreed with m.odern writers on mutation; but differed from them, as has been already abundantly shown, in the magnitude assigned to the variations form­ing the steps of the onward march of evolution. H is observation and study of nature led him to the conviction that large variations, although abundant, were rarely selected, but that evolu­tion proceeded gradually and by small steps,­that it was " continuous," not " discontinuous."

In his presidential address ~ to the British As­sociation at Cape T own in 1905, Sir George D arwin brought forward the following argument from analogy against the " continuous transf or­mation of species " :-

" In the world of life the naturalist describes those forms which persist as species; similarly the physicist speaks of stable configurations o r modes of motion of matter; and the politician speaks of States. T he idea at the base of all these conceptions is that of stability, or the power of r.esisting disintegration. I n other words, the degree of persistence of permanence of a species, of a configuration of matter, or of a. State

• Devel-Opment and E1ioluti-On. J. 1\1. Baldwin, New York, 190.\l, p. 350.

• Report BriUsh A ssociatwn, 1905, p. 8.

50 FIFTY YEARS OF DARWINISM

depends on the perfection of its adaptation to its sur­rounding conditions."

After maintaining that the stability of states rises and declines, culminating when it reaches zero in revolution or extinction, and that the physicist ,vitnesses results analogous ,vith those studied by the politician and the historian, the author continues:-

" These considerations lead me to express a doubt whether the biologists have been correct in looking for continuous transformation of species. Judging by analogy we should rather expect to find slight con­tinuous changes occurring during a long period of time, followed by a somewhat sudden transformation into a new species, or by rapid extinction.H 1

I do not, of course, doubt that there is reality in the analogy between the evolution of states and of species, but it is not, I submit, close enough to justify the author's reasoning from one to the other. T he communities of the social H ymenoptera present much closer analogies with political states, and yet even here it would be unjustifiable to infer that the evolution of insect societies has been discontinuous.

• The following footnote is appended to Sir George Darwin's address:-" If we may illustrate this graphically, I suggest that the process of transformation may be represented by long Jines of gentle slope, followed by shorter lines of steeper slope. The alternative is a continuous uniform slope of change. If the former view is correct, it would explain why it should not be easy to detect specific change in actual operation. Some of my critics have erroneously thought that I advocate specific change per salt;wm.,"

I n reply to this note it may be pointed out that "1,0,· sa/1;11nn evolution" or " discontinuous evolution" differs from "continu­ous evolution " only in the steepness of the slope of change.

FIFTY YEARS OF DARWINIS~·I 51

The analogy seems to me far looser between the changes of configuration of matter ,vitnessed by the physicist and the modification of a S!Jt:Cies as a result of the struggle with its organic environ­ment. The essential characteristics by which the evolutionary history of the organic world di­verges ·widely from that of the inorganic is very clearly stated in the follo,ving brief passage from a letter 1 ,vritten by Charles Dar,vin to Sir Jo­seph Hooker, on November 23, 1856, just three years before the publication of the Origin:-

" Again, the slight differences se~ected, by which a race or species is at last formed, stands, as I think can be shown ( even with plants, and obviously with animais ), in a far more important relation to its associates than to external conditions. Ther,efore, according to my principles, whether right or wrong, I can not agree with your proposition that time, and altered conditions, and altered associates, are ' convertible terms.' I look at the first and last as far more important, time being important only so far as giving scope to selection."

THE FIFTIETH ANNIVERSARY OF THE ORI GliY OF SPECIES;-A RET ROSPECT

T hat the Origin of S pecies, which D arwin de­scribed as undoubtedly the chiief work of his lif e,2 should have been bitterly attacked and misrepre­sented in the ea1rly years of the last half century, is quite intelligible; but it is difficult to under­stand the position of a recent writer who main­tains that the book exercised a malignant influ-

• Life and Letters, II, p. 87. • Life and Letters of Charles Darwin, I, p. 86.

5~ FIFTY YEARS OF DARWINISl\1

ence upon the interesting and important study of species and varieties by means of hybridism. As regards these researches its appearance, we are told, " was the signal for a geneTal halt "; 1

upon them Natural Selection " descended like a numbing spell ' 1

; • and if \ve are still unsatisfied with his fertility in metaphor the autlhor offers a further choice between ithe forty years in the wil­derness, 3 and the leading into captivity.•

Francis Galton, in his address as a recipient of the Dar,vin-W allace medal on J uly 1st last, recalled tl1e effect of the Linnean Society Essay and the Origin. The dominant feeling, he said, ,vas one of freedom. This liberty ·was offered to the student of hybridism as freely as to any other. No longer brought up against the blank wall of special creation, he could fearlessly follow his re­searches into all their bearings upon the evolution of species. And this had been clea1·ly foreseen by D arwin when, in 1837, he opened his first note-book and set forth the grand program which the acceptance of evolution would unfold. H e there said of his theory that " it ,vould lead to study of . . . heredity," that "it would lead to closest examination of hybridity and genera­tion." I n the Origin itself the admirable re­searches of 1(-olreuter and Gartner on these very subjects Teceived the utmost attention and were

' Report BriUsh Associ«tion, 1904, p. 515. • L. c., p. 576. • Mendel's Pri11ciples of Heredity, \V. Bateson, 190:!, p. 104. • L. c., p. !208.

FIFTY YEARS OF DARWI NISM 53

brought before the ,vorld far more pro1ninently than they have ever been either before or since. F urthermore, the only naturalist who can be de­scribed as a pupil of D arwin's was strongly ad­vised by him to repeat some of Gartner's experi-1nents.1 I t is simply erroneous to explain the neglect of such researches as a consequence of the appearance of the Origin and the study of adaptation. So far fron1 acting as a " nu1n bing spell " upon any other inquiry, adaptation itself has been nearly as much neglected as hybridisn1, and for the same reason-the dominant influence upon biological teaching of the illustrious con1-parative anatomist H uxley, D ar,vin's great gen­eral in the battles that had to be fought, but not a naturalist, far less a student of living nature.

The momentous influence of the Origin upon the past half century, as ,vell as that strange lack of the historic sense ,vhich alone could render pos­sible the compa1risons I have quoted, require for their appreciation the addition of yet another metaphor to the series ,ve have been so freely offered.

The effect of the O1·igin upon the boundless domain of biological thought was as though the sun had dispelled the mists that had long en­shrouded some vast primeval continent. It might then perhaps be natural for some primitive

'Darwin's Jetter of December 11, 186i, to John Scott, c,ontains the following words: " If you have the means to repeat Gartner's experiments on variations of Ve,·bascu,n or on maize (see the Origin), such experiments would be precminently important."

54 FIFTY YEARS OF DARWINIS:i\'I

chief to complain of the strong new light that was flooding his neighbor's lands no less than his own, thinking in error not inexcusable at the dawning of the intelligence of mankind, that their loss must be his gain.

And now in my concluding words I have done with controversy.

Fifty years have passed away, and ,ve may be led to forget their deepest lesson, may be tempted to think lightly of the follies and the narrow­ness, as they appear to us, of the times that are gone. This in itself would be a na:i:ro,v view.

The distance from which we look back on the conflict is a help in the endeavor to realize its meaning. Huxley's Address on The Coming of Age of the Origin was a prean of triumph. Tyn­dall, his friend, further removed from the strug­gle by the nature of his lif e-\\•ork, realized its pathos when he spoke in his Belfast Address of the pain of the illust1rious American naturalist ,vho was forced to recognize the success of the teachings he could not accept,-the naturalist ,vho dictated in the last year of his life the unalterable conviction that these teachings ·were false.

I name no names, but I think of leaders of organic evolution in this continent and in Europe, - sons of great men to ,vhom the ne,v thoughts brought the deepest grief, n1en ,vho struggled tenaciously and indomitably against then1. And full many a household unkno,vn to f an1e ~vas the

FIFTY YEARS OF DARWINISi\1 55

scene of the same poignant contrast, was torn by the same dramatic conflict.

W e have passed th1·ough one of the ,vorld's mighty bloodless revolutions; and now, standing on the further side, we survey the scene and are compelled to recognize pathos as the ruling feature.

The sublime teachings which so profoundly transformed mankind ,vere given by H im who came not to bring peace on earth but a sword. And so it is in all the ages with every high cre­ative thought which cuts deep into "the general heart of human kind." It must bring ,vhen it comes di.vision and pain, setting the hearts of the fathers against the children and the children against the fathers.

The ,vorld upon which the thoughts of D ar­,vin ,vere launched ,vas very different from the world to ·which ,vere given the teachings of Gal­ileo and the sublime discoveries of N e,vton. The immediate effect of the first, although leading to the bitter persecution of the great Italian, was restricted to the leaders of the Church; the influ­ence of the second was confined to the students of science and mathematics, and was slow in pene­trating even these. Nor did either of these high achievements of the human intellect seriously affect the religious convictions of mankind. It was far otherwise ,vith the teachings of the Origin of Species; for in all the boundless realm of phi­losophy and science no thought has brought ,vith

56 FIFTY YEARS OF DARWINISM

it so much of pain, or in the end has led to so full a measure of the joy which comes of intel­lectual effort and activity as that doctrine of Organic Evolution which will ever be associated, first and foremost, with the name of Charles Robert Darwin.

THE THEORY OF NATURAL SELEC­TION FRO:tlf THE STANDPOINT

OF BOTANY BY

JOHN l\:I. COULTER

THE indebtedness of Botany to Charles Dar­·win extends beyond his formulation of the theory of the origin of species by Natural Selection. H is historical position in plant physiology and in plant ecology is one of first rank, "vhich these phases of Botany have often gratefully ackno"rl­edged. As for the theory of Natural Selection, its relation to the development of modern plant morphology is still more fundamental. It is true that about ten years before the appearance of the Origin of Species, Hofmeister had given to modern plant morphology its first great impulse in his demonstration of the essential relationships among higher plants; but the announcement of the theory of Natural Selection suggested a modus operandi for the plant phylogeny that m:ay be said to have been established. Among plants, the facts and an outline of phylogeny for the application of any theory of descent had been secured, so that J\T atural Selection came to plant morphology at the psychological moment. It is no wonder that it was received by plant mor-

67

58 NATURAL SELECTION FROM

phologists with eagerness, and that it stimulated tremendously the type of investigation initiated chiefly by Hofmeister. Whether Natural Selec­tion stands or falls as an adequate explanation of the origin of species, there can never be any doubt as to the breath of life it infused into the young science of phylogenetic plant morphology.

I am in no position to state whether from the standpoint of Botany the theory of Natural Se­lection presents any more difficulties or probabil­ities than it does from the standpoint of Zoology. The literature of the theory in its application to animals is so vast, and has become so special, that no botanist can be expected to compass it intelli­gently. The present series of papers may make this situation clear; and yet I cannot presume to speak for botanists in general, among ,vhom there is great diversity of opinion. I can only express the opinion of an individual botanist ·who has had some experience in dealing with the facts that enter into the construction of phylogenies.

SELECTION DOES NOT ORIGINATE CHARACTERS

When the botanist confines his attention to a wide-ranging genus of numerous species, as the genus Aster in North America, for example, the origin of these species by Natural Selection would seem to be an adequate explanation of the situation. The variations are endless and in

THE STANDPOINT OF BOTANY 59

every direction, the intergrades are innumerable, the habitats are exceedingly diverse, and Natural Selection ,vould seem to necessitate just the re­sult observed. In fact, the greatest American student of the genus, after a prolonged effort to detect and define the boundaries of its species, gave it as bis private opinion that "there are no species in Aster." Of course this must be under­stood as an expression of despair rather than of belief, but it emphasizes the situation. With the ,vide-ranging genera showing this condition, it was not difficult to imagine that the sharp differ­ences among isolated species are to be explained by the breaking up of their continuity; and so all species ·were s,vept into the category of Natural Selection.

On the other h.and, "'hen the botanist came to enlarge the horizon of his observation, and in­cluded the whole phylogeny of some great group of plants, or even the phylogeny of the whole plant kingdom, he began to have doubts as to the adequacy of Natural Selection as an explanation of all the changes. He has learned to regard this selection as a factor that perpetuates and perhaps develops certain characters, and that eliminates others; but he cannot discover how it can really originate ne,v characters. The genus Aster, for example, is defined by a definite group of char­acters; and the species may be regarded as the selected variants of these same characters. The pattern changes, as in the kaleidoscope, but noth-

60 NATURAL SELECTION FROi\1

ing new has entered into any combination. But when the Aster boundary is crossed, and still more when the boundaries of Compositre and then of Angiosperms are crossed, absolutely new characters are 1net on every hand; and still the phylogenetic connections seen1 convincing. For example, perhaps no plant morphologist doubts in these days that at least some of the Gymnosperms are phylogenetically related to ancient ferns. The distinguishing mark bet,veen the t,vo groups is the absence of seeds in the one and their presence in the other. The seed and all that goes ,vith it is a ne,v character, and how selection could have originated it, is a question at whose ans,ver even scientific imagination balks. It is evident that the ovules of Gymnosperms are related by de­scent to the sporangia of ferns in son1e ,vay, but so extensive a change does not s,eem to come ·within the possibilities of Natural Selection. We have relatively primitive ovules, but they are enormously different from fern sporangia; and we can imagine how selection may have trans­formed these ovules into those of more advanced type, for this is only manipulating a structure .already in existence and is adding nothing ne,v. The leaves of sporophytes, the vascular system, ihe root system are further illustrations of the same kind. Absolutely unrepresented in the lo"1er groups, they are ne,v, co1nplex, and fully functioning structures ,vhen we 1neet them first. Of cou1·se lost records and an inconceivable lapse

THE STANDPOINT OF BO'.rANY 61

of ti1ne are the usual ans,vers, but they do not save us from doubt.

In brief, by the botanist ,vho has brought to­gether a " 'ide range of material, natural selection might be accepted as having variously arranged a group of established characters, and in this sense given rise to what we call species; but it could not be accepted so easily as originating such ne,v characters as distinguish great groups. In a certain sense, of course, there is nothing ne,v, or else there would be no phylogeny; but as we use the ,vord character, it often appears as a new tiring in passing from one great group to another one presumably derived from it.

NON-ADAPTIVE "ADAPTATIONS"

To the botanist, the greatest immediate diffi­culty ·with Natural Selection !has probably come from the idea of adaptations associated with it. For a time he was captivated with the idea, and much botanical literature testifies to the fact. As he then understood it, nature selected those forms that are best adapted to their environment, and destroyed those that are less adapted. This meant that the characters of the forms selected for survival must show some fitness for the envi­ronment, and great ingenuity ,vas displayed in explaining this fitness. Then came the ne,v sub­ject ecology and its associate experimental 1nor­phology, and the old explanations began to vanish.

6~ NATURAL SELECTION FROM

For example, the character of thorns ·was said to be selected because their presence was a pro­tection :against grazing animals. Now it is kno,vn that thorns chiefly prevail among plants in regions peculiarly free from grazing animals; and that even if the grazing animals are present the thorns do not appear in the early stages of the plant, ,vhen they are most needed. Conversely, the plants chiefly attaclked by grazing animals are singularly free from thorns. Experimental work has shown that many thorns are a response to poor nutrition, and that they may or may not be­come an established character.

The elaborate stinging hairs of the nettle rep­resent a character th:at according to this view was built up by N atull'al Selection, ,vith adapta­tion as the principle of selection. No,v it is known that the nettle is indifferent to their pres­ence and gets along without them.

It is a ,vell-known fact that many seeds, espe­cially those of arid regions, develop a testa so hard that it interferes ,vith the breaking through of the embryo. In fact, it is becoming evident that if selection is working in these cases it is working towards" over-adaptation." 1

A difficulty is also presented by such structures as the vela1nen of the aerial orchids, as well as by the water-conducting vessels of the vascular system. I n both of these cases the structures do

1 This si tuation has been developed by the irecent studies of the germination of seeds and spores by Dr, ,vJlliam Crocker of the University of Chicago,

'!'HE STANDPOINT OF BOTANY 63

not perfo1m their very important functions until the cells are dead. Just how a group of dead cells, performing a mechanical function, could have been built up by Natural Selection, is hard to imagine; and yet, in the case of the vascular system its presence is a fundamental distinction between two g!l'eat divisions of the plant king­dom.

A striking illustration of the change of view that plant structures are necessarily usef til be­cause they have been selected on account of adap­tation has been developed by a very recent inves­tigation of extra-floral nectaries; which included an examination of 100 species of plants growing in the Botanic Gardens of Buitenzorg, Java. The view in reference to many of these extra­floral nectaries has been that they attract ants, which in turn defend the host plant from its ene­mies. Hence we have such a category of plants as myrmecophiles, or" ant-loving plants." Dar­win himself naturally believed in myrmecophiles, and Kerner included them among his illustrations of protection against "unbidden guests." No,v it appears that any such use for these remark­able organs is untenable; and there are many facts that suggest that they have no definite pur­pose that could be laid hold of as an adaptation. The secretion often begins late in the life of the plant, so that any protection it affords is lacking

' Nieuwenhuis von UxkiHl-Giildenbandt, M.: " Extraflorale Zuckerausscheidungen und Ameisenschutz," A""· Ja1·d. Bot. Bui­ten:i.org, II, 6; pp. 195-327. 1907.

64 NATURAL SELECTION FROn-1

,vhen most needed. In some cases the secretion begins at a very early stage of the plant and soon fails, leaving the maturing and adult plants un­protected. The nectaries secrete spasmodically and are often dry; and the nectar of many forms is avoided by ants and other animals. There is no relation bet,veen mutilated flowers, ants, and extra-floral nectaries. Most mutilated flowers produce as many seeds as those that are not; and the honey-seeking ants are not combative and do not attack other insects visiting their host. If these extra-floral nectaries have been developed and perpetuated by Natural Selection, it is an illustration of the selection of harm£ u[ structures, for they often attract insects of all kinds, which damage the plant in various ways. The investi­gation sho,ved that individual plants which se­crete little or no nectar are less harmed by insects than are those that produce nectar.

It is such work that is playing havoc with the " adaptations " of botanical literature, and is f arcing botanists to see in these various structures inevitable responses to conditions that have noth­ing to do with adaptation. It would be going too far to say that such results destroy absolutely all faith in the selection and development and fix­ing of adapted structures, but they do tend to weaken faith and to demand that every claimed case shall be subject to rigid experimental inves­tigation. That there must be selection no one pretends to deny, so far as I know, but when the

THE STANDPOINT OF BOTANY 65

selection includes unfavorable as well as favor­able characters, it seems to have lost its motive.

And still, behind all this uncertainty as to the selection and perpetuation of small variations, as to ,vhether this kind of indiscriminate selection can result in anything so definite as distinct spe­cies, there is clearly evident the large fact of the evolution of the plant kingdom, which has be­come a more difficult problem than ever before. To observe and explain the small results, ,vhich are the only kind that can be brought under the absolute control of modern investigation, seems to result in obtaining a measuring rod too short to apply to general phylogeny; and the more con­fu.sing are our experimental results, the larger becomes the error that is multiplied by the gen­eral application.

So far as I am acquainted with the opinions of botanists whose ,vork has to do with structures and phenomena involved in evolution, there seems to be a general feeling that Natural Selection does not select individual plants on the basis of some small and better adapted variation, and so build up a character, ,vhich with its associates will gradually result in a closely allied new spe­cies; but that its selection of individuals seems to hold no relation to their usef ul characters. On the other hand, there is general conviction that Natural Selection determines what species shall survive, simply by eliminating those that do not. Applying this to a general phylogeny, Natural

66 NA'TURAL SELECTION FROM

Selection becomes a factor of enormous impor­t ance; for the species that survive determine, within limits, the species to be produced.

NON-UTILITY IN THJE EVOLUTION OF GYll:!NOSPERMS

A general illustration of this point of view may be taken from the phylogenetic relationships among Gymnosperms. This ancient group stands among plants as one of remarkable rigid­ity. Land plants should be more plastic than land animals, for they must remain fixed in a given environment, while animals can shift their environment when the pressure of change comes. A striking contrast between the taxonomic char­acters used by zoologists and those used by bot-· anists is brought out here. Among botanists, the t axonomic characters in most general use are those that respond with least promptness or not at all to changing environment; while among zoologists, as I am informed, the taxonomic char­acters in n1ost general use largely fall in the cat­egory of so-called " adaptation " characters, which had far better be called " response " char­acters. For this very reason, I can easily imag­ine that there should be more supporters of Nat­w·al Selection among zoologists than among bot­anists .

. Be this as it may, Gymnosperms seem to be about the least plastic of land plants, certainly the least plastic of any great group. Even the

THE STANDPOINT OF BO'l'ANY 67

number of chromosomes, whi,ch in some groups of plants may vary from speciies to species, seems to be practically a fixed number in the whole assemblage. There seems to be a1nong them lit­tle or no visible response in nature to changing conditions of the most extreme kinds. It ,vould seem that selection among these relatively inva­riable forms can hardly be more than the accident of cro,vding. Certainly one ,can lay hold of no kind of variation in nature that even suggests the coming characters of another species, much less of another genus or family. And yet the gll'oup as a whole shows that certain distinct evo­lutionary tendencies have been ,vorked out in a progressive way. Students of the group may differ as to the details of the phylogenetic his­tory, but there is no difference of opinion as to its general features. Some of these general fea­tures may be instructive in this connection.

The plant which produces the female sex or­gans, kno,vn as the female gametophyte, is not only in the midst of an ovule invested by a thick integument, but is also directly inclosed by the heavy ,vall of the megaspore that produced it. I f any structure is shut away from the influences of a changing environment, it would seem to be this one. And yet, through the whole series of Gymnosperms, this gametophyte sho,vs a pro­gressive transformation. In the most primitive farms it matures as a relatively large mass of tissue, and late in its history the female sex organs

68 NATURAL SELECTION FROM

(archegonia) appear. In the first stage of its development it consists of a la.rge number of free nuclei; in the second stage walls appear and a tissue is formed; and in the last stage this tissue grows and finally produces the archegonia ,vith their egg. The constant tendency throughout the ,vhole group is to produce the female sex organs earlier and earlier in the history of the gametophyte. A series can be arranged illus­trating the appearance of the sex organs at ,vhat might be called the mature stage of the gameto­phyte, at one extreme; then their appearance at earlier and earlier stages of the tissue develop­ment, until they appear with the first formation of walls; and finally, at the other extreme, the eggs appear at the stage of free nuclei, so that no sex organs are formed. This progressive slipping back of the egg in the ontogeny of the gameto­phyte holds no relation to any advantage that can be detected. Certainly it holds no relation to any advantage in fertilization, for that is a pro­longed process among Gymnosperms, and the pollen tube containing the sperms may live for a season or t-wo in the tissues of the ovule. Taking the group as a whole, this is not a sporadic change, ,occurring here and there; ibut the two extremes I have given are the t-wo extremes of the Gymnosperm phylum. Th.is kind of progres­sive change is beyond the reach of experiment, and its explanation is beyond the reach of imagi­nation as yet.

THE STANDPOINT OF BOTANY 69

T he same kind of progressive change is shown also in the embryo of Gymnosperms. I n the most primitive condition, the first stage of em­bryo formation is extensive free nuclear division ,vithin the fertilized egg; after this, ,valls are formed and the egg becomes filled ,vith tissue, the proembryo. T hroughout the Gymnosperm series there is a steady reduction of the amount of free nuclear division, and with it a reduction of the an1ount of proembryonic tissue, so that finally it occupies a very small portion of the fer­tilized egg. All this change has taken place fur­ther from outside influences than the change in the gametophyte, for the embryo is imbedded in the ga111etophyte.

It may be claimed that these are not the char­acters that taxonomists use in distinguishing spe­cies. This is true, but they are just the charac­ters that distinguish great groups, and represent the advancement of the plant kingdom as a whole. I t so happens that both of the progressive changes noted as occurring among Gymnosperms culminate among Angiosperms.

T he male gametophyte of Gymnosperms shows a similar progressive change, not so steady, but none the less evident. I ts few cells are con­tained within the resistant wall of the pollen grain ,vhich produces it. I n the more primitive condition the vegetative cells are variable in num­ber, but evident; but there is a persistent tend­ency to eliminate them, which reaches comple-

70 NATURAL SELECTION FROM

tion in certain Gymnosperms, and is a constant feature of Angiosperms.

It may be said that in all these cases we are dealing vvith structures that have ceased to be useful, and there£ ore are being gradually elim­inated. No one can say how useful they are, but no one can deny that they are functional. But there is a striking illustration of another sort a1nong Gymnosperms. The suspensor is a con­spicuous organ of the embryo in this group, with a development apparently out of all proportion to its usefulness. In fact, it is a most exagger­ated structure, often becoming closely coiled on account of its extreme length. One would sup­pose that this would! be the first structure eliminated, or at least curtailed, if use£ ulness de­termines suppression. But the suspensor of Gyn1nosperms shows no symptom of suppression throughout the whole group, and still among the heterosporous Pteridophytes belo\v and the An­giosperms above, where the same conditions pre­vail, it sho"vs no such unusual development.

Several illustrations could be taken from Gyn1-nosperms, all of them fundamental in the struc­ture and progress of the group, and none of them in use by taxonomists. lVfy claim is that it may be one thing to pass from species to species within the limits of a s1nall natural group; and a very different thing to pass from one great group to another. I do not doubt that the characters of a genus may have been juggled in a variety of

THE STANDPOINT OF BOTANY 71

,vays to form what we call its species, and that one of these ,vays may have been Natural Selec­tion, ,vith or ,vithout adaptation. Our problem, however, includes more than the origin of species. All of our observation and experimental work in this field is immensely important in demonst1·at­ing the theory of descent, and in showing how the final diversity of species is reached; but the meth­ods for securing this final diversity may not apply and probably do not apply to the establishment of the assemblages of different characters that distinguish the great groups, and that any study of phylogeny sho,vs to have been wrought out by steady and progressive change through all im­aginable changes of environment. Species have been likened to the individual waves that appear on the surface of a choppy sea; if so, the deep­seated changes to which I ref er, and ·which phy­logeny makes so evident, may be likened to the great oceanic currents, whose movement and direction proceed ,vith no relation to the choppy surface.

IS,OLATION AS A FACTOR IN ORGANIC EVOLUTION

BY

DAVID STARR JORDAN

BY isolation, segregation or separation as a factor in evolution, we mean the failure of a por­tion of one group or species to interbreed freely ·with the rest of its kind. Such failure is due to the presence of some barrier which prevents free intermingling of individuals or to so1ne condition or group of conditions ,vhich sets certain indi­viduals off from the mass of their kind. Through separations of this sort race distinctions arise, and in time by the same means the more profound modifications which mark ,vhat we call species. The occasion of divergence in most cases is f ow1d in geographical separation, the " raiimliche Son­derung," on ,vhich such strong emphasis has been justly laid by ~1oritz Wagner. It may again be a separation of some other kind, as segrega­tion, through the occupation of different tracts within the same general area, or seasonal separa­tion, as ,vhen flowers bloom or animals mate at different times of the year. There are also forms of physiological segregation. Self-fertilized plants mate with their neighbors irregularly or by chance, the pure species standing alongside of

72

ISOLATION IN ORGANIC EVOLUTION 73

hybrids or quasi-hybrids. D r. Shull informs us that several such cases occur in the flora of Cali­fornia. A race or species of higher animals may develop dislikes or infertilities ,vith forms other­,vise nearly related. Caton tells us that this is true of deer, which "·ill not cross ,vith other spe­cies unless " demoralized," 01· relieved of race antipathy, by enforced association.

LA,v OF GEOGRAPH ICAL DISTRIBUTION

Free interbreeding tends to unify or obliterate forms ,vhich are fertile ·with each other. I sola­tion in any form tends to check this process, and hence in negative fashion ,vorks to create ne,v ,forms based on distinctions arising through pat­ural variation and retained through heredity. F rom this fact arises the rule that closely related fo1·ms or nascent species do not as a rule inhabit or rather breed in the same area. T his proposi­tion has been te1·1ned by Dr. J. A . Allen " J or­dan's La,v of Geographical D istribution."

T he la,v or generalization has been stated as follows :-

" Given any species (or kind) in any region, the near­est related species ( or kind) is not to be found in the same region, nor in a remote region, but in a neigh­bo1·ing district separated from the first by a bar­rier of some sort, or at least by a belt of country, the breadth of which gives the effect of a barrier."

This law holds good as a general rule among animals. T he only exceptions yet indicated are

74 ISOLATION AS A FACTOR

found among plants in which cross-fertilization is not general, among Protozoa and other low forms in which specific distinctions are unknown or at least obscurely shown, in cases of isolation other than geographical, and in a few cases which seem to be explainable on the ground of re­invasion. It is possible that species once thor­oughly separated through some form of geo­graphical segregation may later invade the terri­tory, the one of the other, without crossing or hybridization. This seems likely to occur among plants, and it is possible among migratory ani­mals also. Taking the world over, re-invasion is probably not a rare phenomenon, although in most cases the invading species may fail to estab­lish itself. In the case of animals dependent on man, we find sometimes a form of political segre­gation, which may lead to the separation of races without actual physical barriers. The races of sheep in England, for example, go by counties. The artificial boundary of a county is a barrier to man, Jrather than to the sheep. In all forms of artificial selection, a corresponding degree of artificial segregation is ahvays implied and, ,vith­out segregation, selection has no effectiveness in race-forming. Nothing, for example, can be done for the race impTovement of fishes, unless these can be segregated in artificial ponds, away from the unselected mass of the species.

I N ORGANIC EVOLUTION 75

THE ,vAY ISOLATION ,voRKS

Isolation, as a factor in evolution, represents the failure of a species to unify itself or to main­tain a homogeneous character among its mem­bers. ,vithin a unified species, each member will be fertile ·with any other of the opposite sex. I n tin1e, the descendants of any one may cross with descendants of all the others, thus bringing all individuals to that degree of common relation­ship implied by membership in a common species. Wherever inter-crossing is checked along any line, a part of the individuals will be set off from the mass, and here divergence at once begins. One cause of divergence may lie in the fact that in each isolated group there is some original de­viation from the average of the common stock, thus giving at the start some slight difference in heredity. But this is purely hypothetical and it is not probable in any special case. Other and apparently more potent causes of divergence lie in the difference of experiences to ~vhich each group is exposed. The stress of the struggle for existence is never quite the same in different lo­calities, and the nature of selection must vary accordingly.

That notable differences obtain in time, even in pure stocks, and when there is no visible reason for change, is clearly shown in the experience of stock breeders. Of this, a typical example will suffice. Da1"vin tells us that the t,vo flocks of

76 ISOLATION AS A FACTOR

Leicester sheep, those of Mr. Buckley and of Mr. Burgess, were "purely bred from the original stock of Mr. Bakewell for fifty years." There is not a suspicion of a single instance of deviation from the pure Bake,vell Leicester breed in either flock. Yet after fifty years the difference in the flocks of sheep is so gTeat that they " have the appearance of being quite different varieties." In natu1·e, as in domestication, individuals of the same race, animals or plants, prevented from inter-crossing for a long time, present at least the appearance of distinct varieties or species. A study of the weeds of the ,vorld, as they have spread from place to place, should sho·w this fact in interesting fashion. It can also be shown by a comparative study of dogs or horses. l\1r. Vernon Bailey tells n1e that in the pouched gophers and other rodent groups each valley has its individual peculiarities, those sho,vn in the skulls as well as in the forms or colors of the ani­mals. All these variations, too small to justify the use of technical names, form the beginnings of diffe1·ence in subspecies. '\Vith 1nore perfect isolation these charaicters ·would soon assun1e greater importance. They see1n to indicate the beginning of species-forming.

So far as species in nature are concerned, we can account for the origin of none of them, except on the ground of the presence of so111e forms of isolation. In those groups of animals or plants which have been 1nost studied, subspecies or vari-

IN ORGANIC EVOLUTI ON 77

eties are recognized only as a geographical lim­itation can be sho,vn.

The knO'wn facts fully justify the statement by D r. A. E. Ortmann that:-

"The four factors named, variation, inheritance, se]ection, and separation, must work together to form different species. I t is impossible to think that one of these should work by itself, or that one could be left aside."

To use a convenient analogy, the movement of organic evolution may be compared to the course of a stream. I solation is the rocky ledge ,vhich does nothing, but whose resistance must deter­mine the direction of the river's flo,v. Selection is the force that drives the stream along, and vaJ·i­ation and heredity lie inherent in the nature of the stream of life itself. All of these are necessary in bringing about the :final result, whatever that 1nay be. With these thel'e al'e doubtless other facts, extrinsic and intrinsic, but in this ,vorld of Yaried contour and of prodigal reproduction, no organism, ,vhatever its heredity or its variat ions, can escape these limiting environmental condi­tions. Whatever takes part in the final result must be a factor in evolution, whether it be an initial factor in variation or not.

I n the belief of the ,vriter, the minor differ­ences which separate species and subspecies among animals and plants, in so far as these are not traits of adaptation ( and 1nost of them are clearly not such ), owe their existence to some

78 ISOLATION AS A FACTOR

form of isolation or segregation. By the effect of some form of barrier the members of one group are prevented from interbreeding with those of another minor group or with the mass of the species. As a result, from difference of parent­age, or difference in selection, or from difference in the trend of development, whatever its cause, local peculiarities arise. " Migration," says Dr. Coues ( and by this he means the shifting of hab­itation), " holds species true; localization lets them slip "; or, rather, localization leaves them in differing conditions in the general process of av­eraging up the mass of the species. The peculi­arities of the parents in an isolated group become intensified by in-breeding. These peculiarities become modified in some continuous direction by the selection induced by the characteristics of the local environment. They may possibly be changed, as some have imagined, in one ,vay or another, by germinal reactions induced by impact of environment. I t may be that change of envi­ronment sometimes excites germinal variation. In any event, a new form is sooner or later inev­itable if the segregation is complete. This ne,v form is never coincident in range with the parent species, nor ,vith any other closely cognate or germinate form. Neither is it likely to be found in some remote part of the earth. The details of its distribution will be determined by the na­ture of the organism and by its relation to its environment. The struggle for existence is a

IN ORGANIC EVOLUTION 79

very different matter in different parts of the world of life. The competition with like forms, the struggle with unlike forms, the compi-omise ,vith hard conditions of life, all these change at every angle, and the character of N atura.l Selec­tion changes with them. The individual animals are mobile, as plants are not. They shift about and occupy their range more perfectly, ,vhile in plants their pollen and their seed have great ad­vantages over animals. With a plant everything depends on where its seed is dropped. J,Vhere an animal is born or hatched is a matter of rela­tive indiff e1·ence. With plants, some seed is sul'e to reach almost every available point ,vithin the range of the species, while the vast majOirity of seeds never have a chance to germinate. All these, and every other point of difference, be­t,veen one group of organisms and another, affect the nature and relative value of the different fac­tors in divergence. They tend also to obscure the laws of distripution. But no law is invali­dated by the occurrence of exceptions which come • under some other rule or law.

The obvious immediate factor in the splitting apart of races or species is, therefore, in all groups, that of isolation. :Behind this lies the primal factor of variation, continuous or discon­tinuous. Fluctuation, saltaition or mutation, all these are one for the purposes of our present dis­cussion. With these come the factor of heredity and the factor of selection, to which we must

80 ISOLATION AS A FACTOR

ascribe all adaptive changes and apparently no others. Selection alone does not produce new species, although it may continuously modify old ones. Usually related species beco1ne modified in parallel fashion by selection. Through adap­tations to special surroundings, selection may produce convergence of characters, of ten of such a character as to give a semblance of J"eal homol­ogy. The selection of the desert gives the horned toad resemblance to the cactus; this deceives no one. But it may give one cactus a deceptive resemblance to another ,vhich is forced to adapt itself to exactly the same conditions.

It is not of ten that one species is distinguished from another by adaptive characters, or by any conceivable difference in fitness to the same con­ditions in life. In this 1·egard all are fit, and the process of natural selection holds each one close to its possible limit so long as conditions re1nain constant.

so:ME ILLUSTRATIONS OF THE RESULTS OF ISOLATION

The formation of differe11t breeds of sheep through isolation and unconscious selection in the different counties of England, as else,vhere de­scribed by the writer, is apparently exactly par­allel with the formation of species in nature. The formation and fixing of new breeds or races through conscious selection is exactly parallel with this, except that in conscious artificial selec-

I N ORGANIC EVOLUTION 81

tion the destruction of the less fit is more drastic than in nature and the segregation of the garden or the flock is more perfect than is ever found in field or forest. There are no natural barriei-s so effective as those which may be reared in field or garden.

The existence of cognate or " geminate spe­cies," as I have else,vhere called them, the one representing the other on opposite sides of some barrier, has been long recognized by naturalists. I n a general ·way such species agree ,vith each other in all the respects ,vhich u sually distinguish species within the genus. T heir differences ap­pear in minor regards, characters of degree, or proportion; traits which we may safely suppose to be of more 1·ecent origin than the ordinary characters marking off species within the group.

I llustrations of geminate species of birds, mammals, fishes, reptiles, snails, crustaceans, in­sects, trees, flowers, are ,vell lkno,vn to students of these groups.

To take familiar examples, each well separated island in the "\iV est Indies has its own form of golden ,varbler. Each island in the E ast Indies has its own forms of reptiles, monkeys, snails, and fresh ,vater fishes. Each island in H awaii has its o-wn species of each genus of D repanine birds; ea.eh forest its o'vvn type of land snails. Each of the three groups of rookeries in Bering Sea has its o,vn species of fur seal. Each section of the Isthmus of P anama has its geminate species of

8~ ISOLATION AS A FACTOR

fishes, representing nearly every genus or sub­genus of the shore-water of Mexico. Each floral region of the northern hemisphere has its char­acteristic form of most of the ,\ridespread genera of trees or shrubs. Wherever a distinct barrier exists, geminate species may be found on the two sides of it, unless for one reason or another one of these forms has failed to maintain itself in the struggle for existence. I f the barrier is imperfect, the two species are likely to intermin- · gle, giving an intergradation of forms. The absence of such connecting series is the only dis­tinction between a species and a subspecies or geographical variety which many naturalists rec­ognize. A subspecies that lives permanently in the same region coincident in range with the species from which it springs is unknown in zoology.

-- ~

DARWIN'S VIEW OF THE ROLE OF ISOLATION

Assuming that this view of the relation of geo­graphical distribution to species-forming is a cor­rect one, it is interesting to note the attitude of Dar\vin in regard to it.

it is clear that D arwin had the bi!!lal concep­tion of the views here set forth. H is o-wn work in South America and that of Wallace in the East I ndies yielded similar conclusions, although with D arwin geograp!hical studies were subordi­nated to other forms of evidence of the transfor­mation of species. I solation Darwin considered

IN ORGANIC EVOLUTION 83

mainly in its static aspects, not as a necessary or at least not a separate factor in evolution. " Each species," he says, "has been produced ,vithin one area and has migrated as far as it could." This staten1ent may be taken as the central fact of our kno,vledge of geographical distribution. The distribution of each species covers the earth except in so far as it is unable to reach distant parts through barriers, or as it has been unable to maintain itself in regions ,vhich it has reached-or as it has, through selection and isolation, been changed in some part of its range into a different species. In this case as else­""'here selection and segregation must work to­gether, the one producing adaptive divergence or adaptive convergence, the other non-adaptive divergence alone.

Darwin quotes from VV allace that " every spe­cies has come into existence coincident in space and in time with a pre-existing closely allied spe­cies." This coincidence is attributed, by Dar,vin and Wallace, to " descent with modification." The language quoted is perhaps obscure, but the meaning of VVallace is clearly a recognition of the mutual relations of geminate species.

Darwin further states: " I do not doubt that isolation is of considerable importance in the for­mation of new species." He goes on to say that: " On the whole I am inclined to believe that large­ness of area is of more importance, especially in the production of species which will prove capa-

84 I SOLAT'ION AS A FACTOR

ble of enduring for a long period and of spread­ing "videly." But he regards past isolation as a factor in this case also, for he says:-

" l\1orcover, great areas, though now continuous owing to ,oscillations of level, will often have recently existed in a broken condition so that the good effects of isolation will generally to a certain extent have concurred.

" In isolation in a, small area, conditions will tend to be uniform, so that natural selection will tend to modify all the varying species throughout the area in the same 01anner in reference to the same conditions."

H e goes on to sho"v that in isolation, inter­crossing ,vith outside individuals ,vill be pre­vented; that individuals ·will be freed from outside competition, a condition favorable or " giving time " for " improvement," that is, for adaptive divergence.

It will be noticed that D ar,vin uses the ,vord " isolation" in its literal meaning of island-resi­dence, and that he does not extend it to include segregation or separation by barriers. Yet a mountain lake or a river basin n1ay be just as much isolated in a biological sense for its ,vater animals as an island is for its land inhabitants. Dar,vin makes no effort to separate t,vo sets of facts. The one is that a great continent or a great sea or a great river ,vill contain at any point more species than a sn1all continent, a small sea, or a s1nall river basin. This is because the large area offers freer access for 1nany different types of organisms. Its less perfect barriers

IN ORGANIC EVOLUTION 85

f avor reinvasion, and each group ,vill have some representatives in all available locations. The other fact is that the forms in the small area tend to be more sharply defined. They are better spe­cies, from the point of view of taxonomy, and the causes of their existence can be better traced. In our current studies of evolution, ,ve are of neces­sity more analytical than Darwin. We would view as separate factors elements which to him were simply phases of Natural Selection. In artificial selection, segregation or isolation was taken by Dar,vin for granted. Natural Selec­tion " ras to Dar,vin the same cause or factor re­lated to natural processes. I n his chapter on Geographical Distribution, Darwin sho,vs an essentially modern grasp of the subject, though ,vithout analysis of the reasons why variations in distribution naturally persist.

Dtn·,vin says:-

" The preservation of favorahle variations and the rej cction of injurious variations, I call Natural Selec­tion. Variations 11eithcr useful nor injurious would be unaffected by natural selection, and would be left a fluctuating clement."

It is clear that the completed process of Nat­ural Selection as here indicated implies seg1·ega­tion also, especially if ,ve are to explain ho,v those forms bearing "fluctuating elements" are to be coordinated as species. It is, moreover, certain that in most groups, probably in all, the charac­ters that distinguish species are these ele1nents,

86 ISOLATION AS A FACTOR

neither useful nor injurious. Unless we use " Natural Selection " to cover both processes, as Darwin certainly would have done, we must as­sign to selection the p1·eservation and intensifi­cation of .adaptive characters, and to segregation the seizing and fixing of the non-useful, usually fluctuating, element. It is, ho,vever, a fact ·well known to breeders that these indifferent or non­useful characters are often or generally more per­sistent in heredity than the traits ·which are plainly adaptive. The slight traits which mark the races of men are in themselves, often not ob­viously, valuable in the struggle for existence. They are mostly ineradicable in such selective breeding as history offers. In like manner the dusky face, and other marks of Hampshire sheep, persist after the adaptive traits of the original breed have been enormously modified by selection in the direction we regard as sheep improvement. But fine or coarse, fat or lean, Hampshire sheep are still Hampshires.

In Darv,rin's view, isolation or segregation was doubtless a feature of Natural Selection, not to be set off against the latter as a separate factor in descent. It is very plain from D ar,vin's o,vn ·words, as ,vell as f ron1 the explicit statement of Francis Darwin, that his main contention was for the reasonableness of the idea of the origin of spe­cies through descent ,:vith modification. ,vhat were the causes of modification, ,vas to him a sec­ondary matter. But he was convinced of the

IN ORGANIC EVOLUTION 87

existence of one such cause, and this one he set foi-th in most effective fashion. Without selec­tion, the other life-forces known in his day could not be imagined to lead to any evolutionary re­sults. We are to-day in the same condition. If we exclude selection from our category of forces, ,ve imagine a.n evolution ,vithout motive force, an evolution which would bring about no result. But in Darwin's mind, Natural Selection ,vas the cognate of artlf.i.cial selection. At bottom they were to him the same thing, and segregation a necessary element in both.

Natural Selection was contrasted to supe1·nat­ural selection or special creation, a theory by ,vhich knowable facts were referred to unknow­able causes, operations wholly unimaginable in application to details. At present, we have ceased to set off selection as against creation. We agree that all processes are alike natural or alike supernatu1·al, if we consider them in their philosophic aspects.

The origin of a species is as natural as the for­mation of a snow bank, and both are resultants of forces and conditions within the range of our ob­jective study.

POST-DARWINIAN VIE\>VS

As compared with Darwin, the investigator of to-day has more facts at his disposal; better in­sti-uments of precision; less need to heed the opposition of ignorance and bigotry; and greater

88 ISOLATION AS A FACT OR

need for analysis of scientific conceptions. Under these conditions, while not departing in essentials from the position of D arwin, ·we are forced to bring forward isolation as one of the separate factors in the origin of species, and the factor on which the great and growing science of animal and plant geography mainly depends.

Nearly a decade after the publication of the Origin of Species, D r. 111oritz Wagner set forth the factor of isolation, and showed in convincing fashion its fundamental relation to the problem of the 01·igin of species.

Wagner showed plainly that in the study of the evolution of any form we need to know ,,,here it lived, what it did, how it ,vas bounded, and what was its relation to other forms, geographic­ally as .... vell as morphologically. " For me," he says, " iit is the chorology of organisms, the study of all the important phenomena embraced in the geography of animals and plants, which is the surest guide to the kno,vledge of the real phases in the pirocess of the formation of species."

The work of Wagner, a most necessary sup­plement to that of Darwin, has never received the attention it deserves. T his is due in part to the fact that 1nost of our investigators do not travel. T hey kno,v little of animal or plant geography at first hand. They have had nothing to do ,vith species as living, varying, reproducing, adapting, and spreading groups of organis1ns. Another reason lies in vVagner's o,vn attitude of opposi-

IN ORGANIC EVOLUTION 89

tion to Darwinism. He substituted separation, " railmliche Sonderung," for Natural Selection itself, and denied the potency of the latter factor. The t,vo became in his philosophy competing, not cooperating, elen1ents, and this threw on isolation the i.Inpossible task of accounting for all the phe­nomena of adaptation. We may not ascribe to Natural Selection the " Alln1acht," or limit­less po,ver, ,vhich some N eo-Darwinians have ascribed to it, but on the other hand, those who reject it as a · factor in organic evolution can give no rational explanation of the universality of adaptive organs and adaptive traits; no clue to the most universal characters of organic nature as it is.

Certain \vriters urge that neither selection nor isolation are factors in evolution, but rather elements in speciation or species-forming, a proc­ess defined as something distinct from evolution. Selection and isolation, as obstacles in the stream of life, help to split the on-moving group of or­ganisms into different categories or species; but the i.Inpulse of the forward movement is internal, and the changes of evolution proper affect groups as a ,vhole, and are not concerned with splitting them up into species.

This view may be questioned in two ways. It may be untrue as to fact, or it may be a matter of words only. As a matter of fact, we know nothing of evolution in vacua, of progress in life \vithout relation to environment. All forms of

90 ISOLATION AS A FACTOR

life, ,ve kno"v, are split up into species, \vith adaptation to external conditions traceable in every structure. v\T e kno,v of no ,vay in which organisms can become adapted to special condi­tions except by the progressive failures of those not adaptable. Hence we know of no organis1n which has escaped or can escape from the influ­ence of selection, In like manner, as the ,vorld is covered with physical barriers, no organism can escape the form of evolutionary friction ,vhich prevents uniformity in breeding. There must be some degree of " raumliche Sonderung," even in a drop of ·water.

T o admit these facts, and yet to say that selec­tion and isolation are not £actors in evolution, "'ould appear to make the matter a mere question of words. I f by evolution we mean the theoret­ical progress of life, in vacuo, the effects solely of forces intrinsic in organisms, then extrinsic forces or extrinsic obstacles are of course not fac­tors in such evolution. I f ,ve mean by evolution, the actual life movements of actual organisms, on this actual earth, then forces and obstacles are alike factors in modifying change, and both spe­ciation and adaptation as "'ell necessary parts of the process.

We admit the primary necessity of variation and of heredity, but we can conceive of no case of actual animal or plant in the forming of which selection and isolation have not played each a large and persistent part. Among the factors

IN ORGANIC EVOLUTION 91

every\vhere and inevitably connected with the course of descent of any species, variation, hered­ity, selection, and isolation must appear; the first t,vo innate, part of the definition of organic life, the last t,vo extrinsic, arising from the necessities of environment, and not one of these can find leverage without the presence of each of the others. Isolation as the £actor longest over­looked, though to the field naturalist the most conspicuous of the four, must be advanced[ to the post of honor beside the others, not instead of any of them.

THE CELL IN RELATION TO HERED­ITY AND EVOLUTION

BY

EDl\iIUND B. WILSON

I TRUST that my colleagues in this symposium will not suspect me of any intention disrespectful to them if I speak of my O\vn small contribution to it as the voice of one crying in the wilderness. I do not mean to imply by the Scriptural phrase that the cytologist has to announce the coming of a new gospel of heredity or of evolution. He is, to say the least, as much in need of light as are others. I wish only to suggest the so1newhat iso­lated position of the subject assigned to me, deal­ing, as it mainly must, with matters with which Darwin's own work was not very directly con­cerned, and which in their detailed aspects belong mainly to the post-Darwinian period. , i\Tith the notable exception of t he provisional hypothesis of pangenesis Dar\vin made no systematic at­tempt to correlate his own conclusions \vith those towards which cell-research was already tending in his day; and pangenesis was rather a specula­tive construction than an induction from kno,vn cytological facts. Nevertheless my intrusion into this circle may perhaps be justified on two grounds. One is the keen interest in the inter-

92

HEREDI'l'Y AND EVOLUTION 93

·nal mechanis1n of heredity every,vhere shown by Dar'l-vin in his remarkable chapter on pangenesis and attested by many passages in his private let­ters. The other is the now general admission that the mechanism over ,vbich Dar,vin so long p ondered is to be sought in the organization of the germ-cells.

PANGENESIS AND THE PRINCIPLE OF GENETIC CELLULAR CONTINUITY

Of the original hypothesis of pangenesis I shall say but a few words. Darwin says in one of his letters that he had considered it for up·wards of five-and-twenty years. It is easily the most ab­stract and speculative portion of all his writings. I t ,vas published against the advice of his trusted friend and counselor, Huxley, ,vho had himself many years earlier written one of the fi1·st and ablest revie'l-vS of the cell-theory that appeared in our language. Dar,vin predicted that pangene­sis ,vould be called a mad dream; and on its pub­lication the hypothesis ,vas, in fact, received for the most part ,vith hostile criticis1n or scanty ap­preciation. In its original form it has been gen­erally abandoned; though one of its principal postulates, remodeled by De Vries to form the hypothesis of "intracellular pangenesis," is still accepted by some biological thinkers. I t is none the less deeply significant that so great and saga­cious a naturalist, one whose life '1-vas so largely given to the study of the external aspects of

94 THE CELL IN RELA'l'ION TO

heredity and evolution, should have found him­self irresistibly driven to look belo-w the surface 0£ these phenomena and should hav,e made so carefully wrought an attempt to picture thei1, physical foundations to his mental viision. His deep-seated conviction that sooner OT later the phenomena would have to be attacked from this side is revealed in a letter ,vritten to Sir Joseph Hooker, in 1868, ,vhere he declares, " I feel sure that if pangenesis is stillborn it ,vill, thank God, at some future time reappear, begotten by some other father and christened by some other name." That this prediction still a,vaits fulfilment need not here concern us. What is significant is the attitude to,vards the general problem that it re­veals. And the modern cytologist, therefore, de­spite his failure to find support for Dar,vin's par­ticular conception, has a right to feel that his efforts to analyze the cellular mechanism of heredity would be vie\ved ·with sympathetic inter­est by the great naturalist could he f ollo,v their progress at the present time.

Pangenesis ,vas put for,varcl many years after Virchow had pronounced his celebrated apho­rism " On1r1is cellula e cellula,, ( ,\,J'.lich Dar,vin quotes) , and a full decade after the eminent Ger­man pathologist had insisted on the " eternal law" of genetic continuity by cell-division. Dar­v,rin neve1·theless admitted this la,v unreservedly only in the case of plants, and ,vent no further than to recognize its ,vide prevalence among ani-

l-IEREDITY AND EVOLUTION 95

mals. I n both cases he assumed that in addition to the powers of division cells multiply by means of minute germs or " gemmules," ·which are thrown off by the somatic cells, collected from all parts of the body to forn1 the sexual elements, and are " ultimately developed into units " (cells) like those from ,vhich they ,vere originaUy de­]l:ived.' Pangenesis thus comprised t,vo princi­pal postulates, both of ,vhich had been in a meas­ure foreshado,ved by the speculations of Bonnet, B uffon, and even earlier writers. One is the particulate or meristic assumption that particular hereditary traits are represented in the germ-cell iby discrete and specifically organized particles, the" gemmules" or" pangens," that are capable of self-perpetuation by gro,vth and division with­out loss of their specific character. The second .assumption is that the gemmules are cell-germs originally produced by the somatic cells; and by t his Da1"vin sought to explain the transmission of somatogenic or acquired characters. Ho,v have these two assumptions fared ,vith the prog­ress of modern studies on the cells?

' The development of the gcmmulcs was supposed to depend on their "union with other partially developed or nascent cells, which precede them in the regular course of growth." Darwin does not make it quite clear whether he assumed that the gemmules actually grow into new cells. .Many passages (like the one placed in quotation marks in the text above) seem open to no other interpretation; but in the case of plants, accepting the universality of di,,ision in them, he concluded that "the gemmules deri,,ed from the foreign pollen do not become developed into new and separate cells, but penetrate and modify the nascent cells of the mother plant." This process, he says, is almost identical with a fertilization of the cells of the mother plant by gemmules derived from the foreign pollen.

96 THE CELL IN RELATION TO

The first has been accepted by many acute bio­logical thinkers as ahnost a logical necessity, and has been developed, especially by vV eismann, into one of the most ingenious and elaborate specula­tive constructions to be found in the ,vhole his­tory of biology. I ts logical grounds need not here be analyzed. I will only emphasize the fact that the conception did not gro,v out of actual studies on the cell, but ,vas an imaginative con­struction, based on the facts of vairiation and heredity. It may be true; but for the present ,ve can only regard it as a kind of symbolism, anal­ogous in son1e respects to the molecular-atomic symbolism of physical science, but of far more doubtful validity. Those ·who find such a sym­bolism useful will encounter no positive obstacle in the known cytological facts-they may even find in them a certain amount of indirect support -but the assumption remains unverified, and is probably unverifiable.

The second postulate of pangenesis is wholly unsupported by either experimental or cytolog­ical evidence. There is not a particle of evidence to sho,v that in the higher forms of liife cells pro­duce gemmules or that the germ-cells are built up by the aggregation of such bodies derived from the somatic cells. The most fundamental contribution of cell-research to the theory of he­redity is the law of genetic continuity by cell­division. Cells arise only by the division of pre­existing cells. And the stream of gro"l>vth and

HEREDITY AND EVOLUTION 97

division by ,vluch the continuity of organization is maintained seems clearly enough to be genetic­ally irreversible. It flow·s for,vard from germ­cell to germ-cell in endless succession. It is peri­odically diverted from the germ-strea1n to fonn the bodies of successive generations of individ­uals. These are made of the same stuff as the stream from which they flow. In each genera­tion the germinal stuff runs through the same series of transformations; hence that reappear­ance of the same traits in successive generations that ,ve call heredity.

This conclusion loses nothing of its force by reason of the fact that in a sexual reproduction or regeneration the ,vhole body may be repro­duced from a fragment, from a s1nall group of cells, or even from a single cell, of the soma. These cells, too, have arisen by division in un­broken descent from the germ-cell; they, too, have been made from the same original stuff; and they, too, hand on by division to their descendants the specific tradition of their lineage. It is true that these cells and the germ-cells alike gro"v by the intussusception of matter from "rithout, that the cell-substance is built from, and its activities modified and controlled by, materials that have been elaborated by other cells. But the \vhole force of the evidence goes to sho,v that their fun­damental basis is determined by genetic contin­uity with that of their predecessors, that some­thing is handed on by division ,vhich holds

98 T H E CELL IN RELATION TO

the cell true to its specific type and builds the incoming food-stuffs into the characterist ic fabric of the species. I need not dwell on a conception with \vhich we are all so familiar. Some of the specific applications of the doctrine may have proved unacceptable, but the advances in our knowledge of the cell are ever adding weight to the fundamental principle of germinal continuity for which so many eminent investigators, from R emak and Virchow to Nussbaum and Weis­mann, have contended. And this p1-rrnciple ob­viously affords the true standpoint from \vhich the phenomena of heredity and development must be viewed.

Fron1 this standpoint \Ve are confronted with four principal questions, \vhich I shall in the briefest possible ·way attempt to consider. (1) What is the physical basis of heredity? (2) How is it transmitted from cell to cell? ( 3) I n \vhat ,vay does it play its part in the determination of the hereditary characters? ( 4) How may it be so modified as to give rise to ne,v heritable char­acters?

THE PHYSICAL BASIS OF HEREDITY

I t is no\v universally admitted that the physical basis of heredity is contained in the genn-cell. Is this ha.sis formed by the entire living energid, or may ,ve distinguish in the cell a particular species-substance or idioplasm, that is at least theoretically separable from the other cell-con-

HEREDITY AND EVOLU'.fION 99

stituents? This question has not yet been an­swered ,vith certainty. The cell-syste1n forms a n enormously complex n1oving equiliibrium, -..vhich must in one "'ay be regarded as a single and indivisible unit. F rom this point of vie,v it may justly be maintained that the basis of hered­ity and of the vital activities generally is repre­sented by the cell-system in its totality. But such a position, philosophically correct though it may be, cuts us off from the possibilities of exact analysis. We have every right to inquire in what ,vay the energies of cell-life are distributed in the system and how they are related; and the ques­tion whether certain elements of the system may p ossess an especial and primary significance for the determination of the cell-activities forms a legitimate part of this inquiry.

I stand ,vitb those who have followed Oscar Hert,vig and Strasburger in assigning a special significance to the nucleus in heredity, and who have recognized in the chromatin a substance that may in a certain sense be regarded as the idio­plasm. This vie,v is based! upon no single or demonstrative proof. I t rests upon circumstan­tial and cumulative evidence, derived fro1n many sources. T he irresistible appeal which it makes to the mind results from the manner in ,vhich it brings together under one point of vie,v a multi­t ude of facts that other,vise remain disconnected and unintelligible. What arrests the attention when the facts are broadly vie\ved is the unmis-

100 THE CELL I N RELATION TO

takable parallel between the course of heredity and the history of the chromatin-substance in the ·whole cycle of its transformation. I n respect to some of the most important phenomena of hered­ity it is only in the chromatin that such a par­allel can be accurately traced. I t is this sub­stance, in the form of chromosomes, that sho,vs the association of exactly equivalent maternal and paternal ele1nents in the fertilization of the egg. I n it alone do we clearly see the equal dis­tribution of these elements to every part of the body of the offspring. In the perverted forms of development that result from double fertili­zation of the egg and the like it is only in the abnormal distribution of the chromatin-substance by multi polar division that we see a physical coun­terpart of the derangement of development. Only in the chro1natin-substance, again, do we see in the course of the maturation of the germ­cells a redistribution of elements that shows a parallel to the astonishing disjunction and redis­tribution of the factors of heredity that are dis­played in the Mendelian phenomenon.

These are perhaps the most striking of a mul­titude of facts that point to,vards the chromatin as the embodiment of specific pri1nordia of deter­mination. We may be sure that the microscope reveals to us but part of the story; but that which ,ve see is not for this reason less significant. Ex­periment has taught us, it is true, that the role of the nucleus in determination cannot he regarded

HEREDITY AND EVOLUTION 101

as an exclusive one. I t is certain that specific factors of determination also exist in the proto­plasm of the egg; it is possible that the same may be true of the spermatozoon. Experiment has demonstrated in the clearest manner that many features of the early development, among them some of the most in1portant, are immediately de­termined by conditions in the egg-protoplasm "vithout direct action of the nucleus. But this fact can be rightly estimated only when the whole genesis of the egg has been taken into account. The researches of recent years have proved that the egg undergoes a long process of development during its ovarian history and in the process of maturation, in the course of which the greater p art of its protoplasmic substances are formed and ultimately segregated in a particular config­uration. I t has thus becon1e more than probable that some at least of the determinative conditions in the protoplasm of the fertilized egg are of sec­ondary origin-that they are the outcome of an antecedent development in which the nucleus has played its part. Important formative protoplas­mic materials are knO'wn to be of nuclear origin. It is possible that all may have such an origin. B ut even if ·we do not go so far as this, even if we .admit that the determinative factors of the nu­cleus constitut e but one element in an activity that properly belongs to the living energid as a ·whole, we still can not close our eyes to the plain Tecord that is "vritten in the history of the nuclear

10!2 THE CELL I N REL ATION TO

substance. I doubt whether any one holds the view, ,vhich son1e of the opponents of the chro­matin hypothesis have endeavored to force upon its adherents, that the nucleus enjoys a complete " n1onopoly of heredity." To ·what extent the chromatin embodies primary factors of deter­mination remains to be shown by further re­search. ,;v e are still too ignorant of the physio­logical relations of the nucleus and cytoplasm to be justified in any attitude of dogmatism on this question. But as a matter of evidence the con­clusion that chro1natin does embody such factors seems at least a probable one. As a n1eans of practical inquiry it is1 [ believe1 a good ·working hypothesis, ,vithout ,vhich we should be deprived of one of our most effective instruments for the analysis of the mechanism of heredity. And re­cent research has, I think, clearly sho,vn that, far from being exhausted as some of its critics would have us believe, this hypothesis is steadily open­ing ne,v possibilities of inquiry.

CELL-DIVISION

Accepting the idioplasm hypothesis, in the sense I have indicated, ,vhat do ,ve kno,v of its mode of transmission? '\Ve may ans,ver ,vith assurance that it is trans1nitted fron1 cell to cell by division; and ,ve may still safely assume, I think, in most cases by mitotic or karyokinetic division, though the direct or amitotic process may play a la.rger role than ,vas f onnerly supposed.

HEREDITY AND EVOLUTION 108

We can but glance at one or two of the most significant features of karyokinetic division. The most striking and telling of these is the contrast so often shown betw·een the distribution of the nuclear and of the protoplasmic elements. With certain exceptions in the phenomena of matura­tion1 which only bring fresh support to the general principle, nuclear division is both quantitatively and qualitatively exactly equal. Protoplasmic division is often both quantitatively and qualita­tively unequal, separating substances that have been proved by precise experiment to be of dif­ferent physiological value. But more than this, the formation and division of chromosomes effect not merely a mass-division of the chromatin but an equal meristic division of its whole substance; and as Wilhelm Roux first urged, we can find no meaning in the whole elaborate process if the chromatin be not composed of qualitatively dif­jf erent elements that require equality of distribu­tion. That such is really the constitution of the chromatin can no longer be doubted by any who are familiar with the evidence. If the chromo­somes be not actually persistent individuals, as Rahl and Boveri have maintained, they must at least be regarded as genetic homologues that are ,connected by some definite bond of individual ,continuity from generation to generatii.on of cells. And the evidence has steadily accumulated to show that the chromosomes exhibit definite qualitative differences. In many animals and

104 THE CELL I N RELATION TO

plants constant differences of size, in some cases also of form, are shown among the chromosomes. Specifically different classes of chromosomes can in some cases be distinguished, ,vhich show con­stant and characteristic peculiarities of behavior in respect to some of the most important opera­tions of the cell. The probability is increasing that individual chromosomes possess a particu­lar significance for the development of particular characters. I t has become probable that sexual dimorphism in general is determined by a differ­ence of nuclear constit ution bet,veen the sexes. In some groups of animals the sexes differ in respect to one or more particular chromosomes. In a more general way, Boveri's experiments have proved that abnormal combinations of chro­mosomes lead to falsified forms of development; and these observations give the strongest reason to believe that normal development is dependent upon the normal combination of the chromo­somes.

All these facts are pointing in the same direc­tion. They render the conclusion almost irre­sistible, not only that the chromatin-substance is involved in heredity, but that the chromosomes are composed of specifically different materials, the ensemble of which is essential to normal devel­opment. I t is obvious that the beautiful mechan­ism of karyokinesis is jperf ectly adapted for the meristic division and equal distribution of these materials. The energies that lie behind the for-

IiEREDITY AND EVOLUTION 105

n1ation and action of the karyokinetic figure con­stitute a puzzle for ,vhich, as it see1ns to me, no adequate solution has yet been found. But the effect of its action gives us good reason to regard it as the most important instrument by which the nuclear substance is handed on with its integrity unimpaired fro1n generation to generation of cells.

DIFFERENTIATION

Our third question involves the problem of dif­ferentiation, which is inseparable from that of cell-metabolism in general, since it involves the mode of interaction of nucleus and protoplasm. I t is a significant fact that visible structural clif­ferentiation affects the protoplasmic substance in far greater degree than the nuclear. Both in their structure and in their modes of activity the most important characteristics of different kinds of cells are found in the protoplasm. To some extent, no doubt, the nuclei of different tissues sho,v certain characteristic peculiarities, and these can in a measu1·e be correlate,d ,vith the function of the cells. I t is nevertheless obvious that the most characteristic features of the muscle-cell, the nerve-cell, or the gland-cell are displayed in the protoplasmic rather than the nuclear sub­stances. And this again falls into line with the view that the nucleus is the main conservative element of the cell-system, the protoplasm the plastic element through t he modifications of

106 THE CELL IN RELATION TO

which the cell adapts itself to the performance of the varied special conditions of cell-life.

In considering the problem of differentiation we are therefore led to inquire in what manner the nucl,eus may be conceived to operate in the determination of specific modes of protoplasmic change. De Vries and 1nany of his follo,vers have supposed that control of the cell is effected by an actual migration of organized gemmules or pangens from nucleus to protoplasm. But do we really need to employ the pangen symbolism in the consideration of this question? It seems a sufficient basis for our practical attack on the problem to assume that the control of the cell­activities is at bottom a chemical one and is effected by soluble substances that may pass from nucleus to protoplasm or from protoplasm to nucleus. Certainly it is to such a vie,v that very many of the chemical and physiological studies in this field are no,v unmistakably pointing. The opinion iis gaining ground that the control of de­velopment is fundamentally analogous, perhaps closely sinular, to the control of specific forms of physiological action by soluble fern1ents or en­zymes. Experiment has established the fact that certain forms of development are thus controlled by substances, the " hormones," that may be ex­tracted from the cells that produce them, and upon injection into the body call forth their char­acteristic results. Such an effect, for instance, is the development of the cock's comb in the hen

l-IEREDITY AND EVOLUTIO·N 107

upon injection of testic-extract and its recession to the characteristic female condition upon cessa­tion of the injections, as recently described by , i'\7 alker. Analogous phenomena are seen in the ,vell-kno,vn effects of thyroid extracts, or in the effect upon the 1nam.mary glands of injection of extracts of the f etus, as described by Starling and Lane-Claypole.

,;v e are thus. led to so1nething more than a sus­picion that the factors of determination, and therefore of heredity, are at botton1 of chemical nature. It is a ,vell-kno,vn fact that correspond­ing tissues of different species often show char­acteristic chemical differences; and to some extent the same is kno,vn to be true of the germ-cells. T he conclusion thus becomes highly probable that the characteristic differences of metabolism be­tween different species, including those involved in development, are traceable to initial chemical differences in the germ-cells. I n so far as the chromatin theory expresses the truth, the pri­mary basis of these differences may be sought in the nuclear substance. There is good reason to believe that some at least of the enzymes are of nuclear origin. It seems a pro1nising hypoth­esis that the chromosomes may be regarded as self-perpetuating magazines of specific sub­stances, similar in nature to the enzymes or their chemical antecedents, that play an essential role in the determination of the cell-activities, includ­ing those involved in development. From this - . -.. - -

108 THE CELL IN RELATION 'l' O

p oint of vie,v the fertilization of the egg might almost be compared to an intracellular injection of enzymes.

The apparent simplicity of such an hypothesis should not delude us into the belief that it touches the root of the matter. I t presupposes a specific " organization " of the chromosomes of ·which ·we know nothing, and upon which must depend the perpetuation of their characteristic chemical con­stituents. I n this direction ·we are thrown back upon purely speculative constructions which it would be unprofitable to follo\v out here. But so far as the hypothesis goes it seems to offer a really practical point of attack for the chemical study of differentiation and heredity. I n the Mendelian phenomenon ,ve see a synthesis, split­ting apart, and recombination of determinative factors that is singularly like that of chemical ele­ments or radicals. In the l\1endelian heredity of color, £or instance, the orderly resolution by the germ-cells of compound pigment-producing factors into simpler ones, their recombination to form new compounds, the intensification or dilu­tion of col or by specific and separable factors, the production of particular colors by mixing to­gether factors ,vhich are singly incapable of pro­ducing color- in all this we see a series of oper­ations that show an astonishing similarity to the procedure of the chemist in his laboratory. That such things are possible in the case of relatively simple characters, such as colors, gives strong

HEREDITY AND EVOLUTION 109

ground for the belief that similar operations are concerned in the production of more complex characters. Those who hesitate to dra\v such a conclusion may well reflect upon the remarkable eft'ects of the " internal secretions " of the en­zymes and hormones, and upon the extreme sus­ceptibility of the developing embryo to even very slight chemical changes in the surrounding me­dium. It is my belief that in the direction here indicated lie the greatest possibilities of future investigations upon the cell, and that in the union of cytology and biochemistry lies our greatest hope of future advance.

HEREDITY AND EVOLUTION

Lastly, if we accept the ,vorking hypothesis that the primordia of determination are chemical in nature, ho,v may we conceive them to be so modified as to produce ne\v characters? It seems to me that this question may ,vell be reversed; for the ,vonder is, not that the idioplasm changes, but that it adheres so stubbornly to its type. It may as ,veil be admitted that both our cytological and our chemical knowledge in this direction is prac­t ically nil. It is well, further, to speak a word of caution at this point. We must not forget that some of the most acute and thoughtful of naturalists have in recent years expressed the conviction that the ultimate control of develop­ment is not to be sought in the physico-chemical properties of the germ-cells, hut in an indwelling

110 THE CELL IN RELATION TO

" t 1 h " " 'l d l . " f en e ec y or e an e a vie, a power o un-known nat ure, that may, in the last analysis, be psychical jn nature. But, profoundly interest­ing as some of these vitalistic speculations are, ,ve are bound to hold fast to the physico-chemical and mechanistic hypothesis of heredity until the pos­sibilities of observation and experiment in this direction have been exhausted. I f there be a physico-che1nical basis of heredity ,ve should ex­pect to find it capable of modification by physico­che1nical agencies; and so much, at least , is kno~rn to be the fact. I t has been abundantly demon­sti-ated that both the body-cells and the germ­cells react to changes of the environment by def­inite physiological and morphological changes. Many experin1enters have demonstrated the ex­treme susceptibility of the discharge,d eggs or spermatozoa to even very slight chemical and physical stimuli. We can not doubt that they are equally sensitive to stimuli ,vhile still ,vithin the body, and at every stage of their development. T he almost unique experirnents of MacD ougal on the higher plants seem to sho,v that direct ,ehenlical treatment of the germ-cells 1nay pro­duce definite and irreversible effects upon the off­spring. Those of To,ver on the insects, though less direct, are hardly less convincing.

Though ,ve may not fully understand the man­ner in ,vhich the germ-cells are modified, there is no inherent improbability or difficulty in the con­ception that such n1odifications ,vill produce bias-

HEREDITY AND EVOLUTION 111

togenic variations or mutations that are inherited, permanently or temporarily. We can readily understand that the constitutional effects of tem­perature, food, moisture, and similar general agencies of the environment may manifest them­selves in definite changes that reappear in follow­ing generations because the ger1n-cells have been directly affected in the same way as the somatic cells. It is natural to suppose that the idioplasm possesses a slight instability of chemical or molec­ular composition that results in corresponding fluctuations or indefinite variations of the adult, ,vhich may or may not be inherited. We find no difficulty in the conception that the idioplasm may undergo considerable, sudden, and irre­versible changes which produce mutations of greater or less degree. We can comprehend how particular constituents of the idioplasm may change ,vithout affecting others, thus giving rise to mutations in respect to only a single character or a particular group of characters. We can con­ceive the idioplasm as w1dergoing a slow secular change that results in continual divergence in many directions or in a definite orthogenetic line of transformation. But in respect to the trans­mission of acquired characters the old difficulty confronts us to-day as formidable as when it was first fairly revealed to us through the argument of W eismann. What is really difficult to com­prehend, what I think we can not really conceive if pangenesis be discarded, is ho,v the idioplasm,

..

11~ TI-IE CELL IN RELATION TO

or the germ-cell as a whole, can be a storehouse of specific and detailed somatic impressions which cause the reappearance of similar somatic effects in generations to come.

Darwin's ingenious attempt to picture such a process was a legitimate speculation, worked out ,vith a power and insight that should stir enthu­siasm in even the most skeptical of critics. More than this, it still remains, as I think, the only in­telligible hypothesis of the transmission of ac­quired characters, as Dar,vin understood the plu:ase. But it finds to-day little or no real sup­port in the results of observation and experiment. Attempts have been made to substitute for Dar­,vin's migrating gemmules soluble internal secre­tions-hormones or other substances-that are produced by the various. organs and transmitted to the reproductive organs through the fluids of the body. Heredity has been compared, and with justice, to an " organic me1nory ,., ; and this has been assumed to be a property of the organ­ism as a ,vhole, irrespective of the distinction be­tween germ-cells and soma. It has been urged that the heredity of acquired characters is n1ore readily conceivable if the incre1nents of change be small and extended through long :periods of time. Any or all of these things are possible; but let us not deceive ourselves. Does any of these assumptions really lessen the difficulty or give us a clear mental picture of ,vhat must occur if the heredity of acquired characters be a fact?

HEREDITY AND EVOLUTION 113

I do not see ho,v. Inability to form a clear a priori conception of the process has in itself no validity as an argun1ent against the fact, if fact it be. The progress of biological discovery has repeatedly transfortned apparent a priori impos­sibilities into everyday realities. And if exper­iinent shall really demonstrate the transmission of somatogenic modifications the cytologist has no fundamental obstacle to interpose. The mechanism that his studies have revealed will ac­count for the transmission of all forms of ger­minal modifications, ho"'rever they may be caused. The question involved is not of the transmission of the idioplasm or of the germ-cell, but of its interaction ,vith the soma; and this is not an a priori question, but one of fact. L et us admit freely that such an interaction as Dar,vin as­sumed n1ay be a real and potent factor in hered­ity, though it gives no hint of its existence in the visible apparatus of the cell. In the present defective state of our knowledge we may well grant that the1re may be many a thing between gern1-cell and body that is not yet dreamed of in our biological philosophy. But has the trans­mission of acquired characters, in the strict and proper sense of that much abused phrase, been demonstrated? If in closing I venture to, ques­tion this, I pray that my sins be not visited upon the study of the cells, but upon a failure t o dis­cover the demonstration in other fields of inquiry.

,

THE DIRECT INFL UENCE OF ENVI R ON1VIENT

BY

D. T . l\fAcDOUGAL

ANY serious consideration of the diversity of organisms, of the complexity of the qualities they bear, of the relationships they sustain, and of the character of the stresses under ,vhich they exist with relation to the environmental setting, leads inevitably t o the conclusion that their evolution­ary development must have been affected by many modifying agencies; that the origination, or activation of their qualities or characters may not be ascribed to any single causal force or guid­ing factor; and that the course of heredity from generation to generation has been determined by many things beside the simple inertia of pri1n­itive initial qualities of p1·otoplasm.

When we join in the accepted generalization that the qualities and forms of organisms now existent are the net result of the actii;in of envi­ronic forces upon ancestral structures, selective as ·well as initiatory, ·we implicate a much larger group of conceptions than that embodied in the present thesis, since it is the intention t o confine discussion to the possibilities that arise ,vhen liv-

114

DIRECT INFLUENCE OF ENVIRONi\fENT 115

ing or self-generating matter transmits its spe­cialized characters from one generation to an­other in the ge1·1n-cell, and displays its periodic somatic expansions in ontogeny.

"\Vithin this definite and restricted field, exact­ness and clearness of comprehension of the rela­tions involved ,vill depend directly upon the thor­oughness ·with "\>vhich ,ve may be able to connect our conceptions ,vith the physico-chemical proc­esses of organisms.

The more in1portant external, direct, or phys­ical factors, the influence of which induces adjust­ments and engages the activities of protoplasm, include radiant energy in its various phases, and the chemical structure of the medium, substratum 01· substances corning into contact ,vith the living matter and included ,vith its intake and output. These agents interlock intimately ,vith the parts of the self-geneTating protoplasmic machine, fur­nishing building material, energy in various forms, catalysts, and control reactions in a man­ner so intimate that it is impossible to think of living matter free fron1 its environic setting.

J\T o,v if we set about the calibration of the quan­titative relation of any of these factors to living matter, or attempt an estimation of the qualita­tive effect, " 'e will find that, ,vith respect to any given strain of organisms or any individual, the constellation of specific activities, processes or functions, grouped in the plant are adjusted in such manner that they proceed at the most advan-

116 TI-IE DIRECT INFLUENCE

tageous rate ,vith relation to each other ,vithin, for example, some narrow range of temperature. In our easy acceptance of the obvious, ·we are apt to assume that these optimal conditions are fur­nished by the native habitats of plants, or in other ,vords, the place they happen to occupy in their movements about the ,vorld when they are called to our attention. Now, on the one hand, plants simply are found in areas they have been able to reach, and " native habitats " may by no means offer the optimal conditions, a condition of affairs of ~,hich more than a hint is furnished by the irruption of ,veeds, f ollo,ved by a development of a vigor unknown ""rithin the pre,rious range of the species. On the other, the reminder is neces­sary that no one habitat n1ay furnish the optima for the accomplishment of all of the processes involved in the ontogeny and reproduction of the individual, and all environic relations include groups of compron1ises and of adjustments that put the capacity of the living 1uatter to the ut­most stresses it may bear.

Two main considerations arise when attention is directed to the behavior of the organism as it encounters the external factors in unusual inten­sities, an experience ,vhich has been countlessly repeated and ,vhich is one of the eliminating fac­tors in selection. The fi1·st concerns the mechan­ism of the adjustment of the individual to alter­ing environment, and the second, the possibilities of transmission of the effects of the adjustment

OF ENVIRON1"1ENT 117

to the progeny, both in functional capacity and acco1npanying structure.

ADJUST,1fENT OF THE INDIVIDUAL TO ALTER­ING ENVIRON:l\IENTS

Let us take, for example, a plant standing in the open in a habitat in ,vhich it is firmly estab­lished, and introduce son1e modifications of wide range of the insolation, which n1ay or may not register ,vith anything previously encountered by this individual. T he primary or direct effect of the change ·will undoubtedly be a modification of the reaction-velocities of some of the chemical processes so that metabolism and all of the life­phenomena dependent upon it ,vill undergo alter­ations in rate, cell-division, chromosomatic invo­lution, catalyptic action involving respiration, intake and excretion, and finally growth also. A secondary effect accompanying these changes will be due to the irritability of the living matter by ,vhich sudden changes in aln1ost any external factor ·will exercise a releasing or unloosing ac­tion. Outward manifestations of such action are seen in the various thermotropic and heliotropic n1ovement of leaves, and 'A'hile there seems to be a disposition on the part of some physiologists to eliminate metabolic activities from the realm of irritable reactions, yet it does not seem justifiable upon present evi.dence.

Whether an irritational phase intervenes or not, when an environment al factor undergoes

118 THE DIRECT INFLUENCE

rapid alteration, the activities affected soon as­sume a fairly steady rate, determined directly by the reaction velocities of the substances con­cerned, and the change goes no further than that of a purely physiological, or, strictly speaking, physico-chemical, accommodation. If the change in question is introduced in the developmental period of the individual, the members and organs not fully mature may take on unusual structures and assume aberrant or variant forms, ,vhile if the resting seed or spore is germinated under altered conditions, all purely irritational re­sponses are eliminated and the entire individual may show a more or less atypic ontogenetic pro­cedure.

This somatic variability in response to environ­ment is a matter of common observation, but de­viations of this character are of but little impor­tance in heredity unless they or their effects are repeated in successive generations. This trans­mission of somatogenically induced characters is the cause of our confusion and the source of our doubts, constituting as it does the essence of the controversy as to the " heredity of acquired char­acters." On the one hand Weismannists predi­cate an isolated current of heredity coursing from germ-cell to gerin-cell, yielding qualities that direct ontogeny, but receiving nothing in return except nutrition and continuance, ,vhile on the other hand a by no means voiceless constituency presse~_f o~:__ th~ acceptance of the conclusion that

OF ENVIRONMENT 119

e,•ery " 'ave of variability and every impress of the environment upon the soma are communi­cated from it to the germ-plasn1 upon "vhich it becomes f oreve1· indelibly engraved. '\i\Then to this clai1n there is added the assun1ption that while the effect of a single external impression may be very slight, its repetition, rhythmically or other­,vise, would finally cumulate to produce appre­ci.able and lasting effects, ,ve have a conception difficult to prove or disprove, especially since it is a ,vell-established fact that 1·epetition of stimu­lation does give cumulative effects in both irrito­motility and variability. The whole question, ho,\1ever, resolves itself into the con1paratively simple inquiry as to the physiological connections and correlations of the so1na and gern1-plasn1. • It is ,vell kno,vn that not all of the various organs or tracts of tissue are directly affected alike by any external factor, a result due to the essential differences of the cells composing t hem. Thus an arid atmosphere or intense insolation " rould affect leaf activities chiefly, ,vhile unusual soil concentrations ,vould influence roots only. The various members of the root and shoot are in close correlation, however, and the activity, growth, and mode of development of organs not directly acted upon by the factors mentioned may be profoundly influenced by the altered products of the organs that are affected.. Thus the wound­ing of a root is reflected by changes in the shoot, the removal of one of the parts of a compound

l~O T HE DIRECT INFLUENCE

leaf causes adjustments in the remaining ones, and instances might be multiplied ahnost indef­initely to show that effects produced in one part are quickly and forcefully transmitted to other p arts of the soma. I t matters not for the pres­ent whether the means of communication be spe­cial tracts, nervous mechanisms, chains of cata­lytic reactions, or what other method of com­munication.

THE ACTION OF SOlvIA UPON GER~l-PLASJ'.\f

Similar communications bet"·een the egg and soma are to be encountered. In some of the car­potropic and gametropic movements of seed­plants, the accomplishments of definite stages in the development of the embryo-sac and fertiliza­tion, result in impulses to stems and peduncles several centin1eters distant, producing move­ments and morphogenic alterations of a very striking character. "\V'ithout further enlarge­ment on this theme it is to be said that the securest foundation is laid for the conclusion that ,vell­de:fined correlations exist in the plant by which secondary effects of the action of external factors, or of morphogenic or embryonic procedure, may be freely communicated from one part of the soma to another, and f ron1 the egg to the soma.

With such a substantial substratum of estab­lished facts, ,ve no,v turn to the problem as to the communication of effects from the soma to the

OF ENVIRONl\,IENT l~l

egg or sperm, in such manner that these effects would be transmitted to succeeding generations.

The n1ost obvious and the most primal relation bet,veen the soma and the egg is the nutritive one, and a revie,v of the evidence offered by Pictet and others leads to the conclusion that the char­acter of the building material supplied to the egg as varied by environmental influences may ,vork changes that pass from one generation to an­other, so that it is indubitably established that the egg is not isolated and possessed of such highly developed selective power that it may avoid the intrusion of unusual substances.

The experin1ents of Oscar Riddle, S. H. and S .. P. Gage,' in which it was sho,vn that Sudan I II, a dye, fed to a hen, results in the coloration of the yolk of her eggs, and that the chicks hatched from such eggs take up the dye from the yolk, which finds a lodgment in their o,vn fatty tissues, are of special interest in this connection.

Actual available evidence does not warrant us in predicating any other form of influence of in­ternal region upon the germ-plasm as it takes form and special activity in the egg and sperm, beyond that of physio-chemical processes orig­inating in the soma. Alterations in these proc­esses ·which might affect the egg and be registered in its hereditary activities might occur at any stage of the ontogeny without direct reference to the time intervening between the reception of the

• Science, !iS: 494. 1908.

122 THE DIRECT INFLUENCE

stimulus and the reception of a possible impress by the egg.

Concerning the results from repetition of stimuli in a series of generations, about the only facts at hand are those obtained from a study of variability as affected by nutrition, in ·which it is found that more favorable conditions of nu­trition increase the range, and that further in­creases accumulate with the continuance or repe­tition of the optimal conditions ,vith 1·elation to successive generations. The foregoing may be taken as a f ~ir representation of the physiolog­ical basis of the possibilities by which alterations in the soma might be impressed upon the germ­plasm and transmitted to successive generations, and a description of the authenticated observa­tions and well-ordered experiments which have been made by skilled wo1·kers in dealing with this subject during the last few decades would form no mean record. I t would entail a historical re­view far too voluminous for the present occasion. Ho"l>vever, among other general features it appears that plants moved to habitats and to cultivated fields to the northward and south,vard have been seen to take on a seasonal rhythm in accordance with the ne,v climatic conditions encountered. Unusual temperatures and foods have caused marked alterations in structure, markings, com­position of the body, periodicity of reproduction and range of adjustment and endurance in both plants and animals, but in all of these cases the

OF ENVIRON1"1ENT 1!23

alteration gradually disappeared when the induc­ing conditions ,vere removed, except in a few instances in which it could not be demonstrated that the germ-plasm had not been directly affected.

Butterflies, moths, fishes, crustaceans, birds, guinea pigs, rabbits, trees, fungi, cereals, and bulbous plants have all been drawn into the ex­perimental field with a remarkable unanimity of negation in so far as the so1natogenic induction of characters ,vas solely concerned, which might be fully transmissible to successive generations not under the influence of the exciting factors. Ten1perature, light, food, and composition of the medium or substratu1n all have been tested in their various effects. Only ,vhen the germ-plas1n has been acted upon simultaneously ,vith the soma has any well-defined reappearance of in­duced characters in succeeding generations been noted, and of the earlier results those of Stand­fuss and Fischer seem most notable, since in ex­periments with Vanessa and Arctia the applica­tion of special temperatures or the modification of nutritive conditions induced the formation of aberrant characters in some of the offspring. The ne,v qualities were displayed in varying degree, and maintained their distinctive appearance in the products of hybridization with the parental strain. There seems to be some doubt among zoologists acquainted with these forms as to the significance of t hese results. I t is not clear as

1~4 THE DIRECT I NFLUENCE

to the 1nanner in which the formation of the new characters was induced. The experimental agen­cies employed affected both the soma and the germ-plasm segregated in the reproductive ele­ments, and no interpretation of the facts would justify the conclusion that the aberrant qualities ,vere somatogenically acquired.

v,Thile failure has attended all efforts to dem­onstrate the continued inheritance of impressions received by the body alone, a number of arrange­ments are found in nature ,vhich seem to demand such action fo1: their explanation. Among these certain rudimentary organs, and also co-adapta­tions in ,vhich simultaneous specialization occur­ring in t\vO or 1nore me1nbers of the body has made for increased fitness, are difficult of inter­pretation without the interposition of somatic induction.

DIRECT STI~IULATION OF THE GER~f-PLASM: IN BEETLES

~1:eaO"while the possibility of influencing hered­ity by agencies acting directly upon the germ­cells has a\vakened the keenest interest among biologists. The relations of soma and germ­plasm make it difficult to induce changes in the body \Vithout affecting the reproductive elements, while it is possible to devise experin1ental meth­ods by which the egg or sperm alone may be sub­jected to 1nodifying agencies. This has been done with such success that some very important

4 .. ;•

-... ( '

' '

PLATE I . FIG. 1. Leptinotarsa nndccimlinent.81 nornrnl form.

F10. 2. Fornt dcri\•cd rrom L. nndccimlmeata thron:;b the application or the climatic condi1iont(. For eon\'cnicnce this form hos been cnHcd nn~ustoviuatn be. c:1usc it most clo~ely resemble& t1 epccil'S dc.:<cr1bed by Jacol>y, but it.differs from :,11~11i:itovin:1u1. In nrnny chnrttctcrB considered irn1>0rhrnt by the €.)'Slematists. (From J'>Jace IG, lnvestigat.ion or Evolution in Chry&omelid Beetle::J of. 1hc gcou:f LcJltinotar.ea. Carnegie Institution, Publication No. 48, 1005. Af1er Tower.)

FIGS. 3. 4. Normal miroeis or nuclei in cells of 1>lont.

Fros. f;. 6, 7, 8. Irregularities or mitosis in cells o f onion roots rc1ulting from expo!'Jure to rndiurn. LA rrnr GAger. J

OF ENVIRON~IENT 125

conclusions may be founded upon the evidence obtained. The results of the ,vork by Tower, in which beetles of the genus Leptinotarsa were subjected to various combinations and alterations in climatic conditions in a series of experiments carried on for a pe1~od of more than t,velve years, have recently been available and far surpass in importance anything previously obtained from animals. The value of the evidence is greatly enhanced by its repetition, by the fact that pedi­greed cultures were used and conditions so regu­lated that an accurate analysis of the effects of the various climatic factors could be made.

Professor To,ver finds that:-

" Not only members of the genu.s Leptinotarsa, but also of allied genera can be directtly modified by the app1ication of intense environmental stimuli to the germinal material. The use of temperature and moisture in unusual degrees of intensity has given rise to a number of forms and modified characters. Some notion of the extent of these modifications is gained from the two fol]owing illustrations. In Plate I, Figure 1, is shown the normal fonn of L. undec·innl-ine­ata, and in Figure 9l, a race derived from it by the application of low temperature and low relative humid­ity. This new form resembles in so1ne respects Jaco!by's species L. angustovittata, and b1:eeds true. It matters not whether this ne1v form is a species, race, elementary species, or a nightmare to the systematist, the important point is, that as the result of subjecting the germinal material to certain conditions at a fixed point in its development, that the eggs thus treated, when fertilized by normal male germs, gave the form shown, which breeds true without subsequent seg1·egation of chaa·ac-

1~6 THE DIRECT I NFLUENCE

ters. I n this case both structural and color char­acters are modified.

" Many other illustrations might be given of the entire change in the colora t ion of body, both in Jarvre or adult, of the modifications of parts and of particular portions of the body or of individual color marks. These arise, some from the treatment of the male germinal ma­terial, some from tteabnent of the female germinal sub­stance, others from a treatment of both germinal ma­terials to the conditions of experiment. In some of the modifications thus induced, the full expression of the change is attained at once in the individuals that develop from the treated germs, and in others it requires one, two, three or more generations to attain the full expression of the n1odified attribute. It does not make any difference whether the full development of the modification is attained at once, or after the lapse of several generations, the behavior is the same, in that there is no regression or reversion to the parental con­dition.

" I n my published work I have given some of the results derived from the application of external factors at one stage of the germ cells. Eggs that have been subjected to the conditions of experiment immediately before the 1naturation period, have given the results now in print and it was from eggs so treated that the race illustrated in this statement came. Analysis of the results from these experiments shows & number of interesting poin t.s.

"First: Not all of the germ-cells are modified, but only a varying proportion of them, which may indicate one of two things; either that there are differences between the eggs in their capacity for modification, or that only certain eggs were in the propel' stage fo_r modification, at the time of the application of the experi­mental conditions. Second: 'l'he results are sometimes modifications all in one direction, nt others they are in many directions, two, three or more different forms arising from the same experiment. Third: The mod-

OF ENVIRONMENT 1~7

ifications in some characters stand apart from the condi­tion of the parents without intexgrades, at other times the same modifications have intergradcs; some charac­ters, as far as known, never have intergrades and some always show them, and there is no place where one can draw a line and say that on one side all are discontinu­ous variations and on the other side they arc continuous. Fourth: The modifications produced never, as far as known, segregate the characters in subsequent genera­tions, indicating a condition different from hybrids. In this respect my results are like those of i\!IacDougal with plants."

Obviously the subjection. of an entire organism to the influence of an enveloping factor implies also its action upon the soma as ,vell as upon the germ, and ,vhile necessarily the possibility of some secondary or parallel inductions a1·e not entirely eliminated, yet an examination of the detail of the experiments points unerringly to the conclusion that the majo1· effect is due to the action of the external agency on the egg or sperm. The soma is indeed the most immediate environ­ment and medium of the germ-plasm, and its activities must interlock most intricately ,vith those of the egg and sperm, in " 'hat manner has already been suggested.

EFFECT OF RADIATIONS ON GERM-PLAS~I

Somewhat easier of analysis are the effects produced by such forms of energy as radiation of known character and measured wave-length as illustrated by the results secured by the use of X-rays, Roentgen rays, and radium emanations.

128 T HE DIRECT I NFLUENCE

In general it may be said that such forms of energy retard growth and compel an incomplete differentiation of tissues when applied to an indi­vidual before maturity, producing serious delete­rious effects if applied afterward. When eggs or sperm are treated by these agents, the most profound disturbances may ensue in the primary divisions, and the ontogeny of individuals aris­ing from a fertilization, either component in which has been subject to such action, shows a destruction of correlations and great disturbances in symmetry, according to the most recent tests of MacGregor with frogs. In most of these cases the disturbances were so great that the indi­viduals concerned were incapable of reproduc­tion, and nothing furthe1r concerning their effect on heredity was possible. The fact that the re­sults were of the same general character, whether the egg or sperm was subjected to the action of the experimental agency, ,vhether held in the re­productive tracts of the animal or "'holly free, is a matter of so1ne impo1tance, since it eliminated the intervention of the soma as a possible source of n1odification of the results.

Recently Dr. C. S. Gager has completed an extensive study of the influence of rAdium on plants so applied that the elements subjected to its action survived and '\\•ere capable of' reproduc­tion. An examination of the effects on the nu­cleus as ,vell as the structure of the soma was made with some highly interesting results.

OF ENVIRON:i\iIENT 1~9

, vhen the root tips of the onion (Allium cepa) ,vere exposed for different periods of time to rays from radium bromide of various degrees of activ­ity, profound alterations ,vere induced in the mitoses of the cells. In nearly all cases the passage of the chromosomes to the poles of the spindle proceeded ·with great irregularity. Fre­quently one or t,vo chromosomes would remain behind near the equator of the spindle, failing completely to take part in the organization of the daughter nuclei (Plate I, Fig. 6). At times several chromosomes or portions of chromosomes ,vould remain at one side of the spindle, or be carried beyond the poles ( Fig. 8), or again be dra,vn out as if subjected to considerable tension (Fig. 5). I n one instance, after the main cell­division ,vas nearly completed, a small secondary spindle, in tardy telephase, ,vas observed at one side of the cell (Fig. 7).

From these :results it ,vas seen that the radium treatment afforded a method by which chromatin elements might be eliminated from reproductive cells, and if these are the carriers of certain spe­cific characters, as indicated by the researches of Wilson, then a ready means of suppression or substitution of characters would be afforded. In addition to these distinctly radical effects, the _chromatin might be modified so as to form the basis of characters not hitherto expressed by the organism.

Proceeding on this basis, Gager exposed to

130 THE DIRECT INFLUENCE

radium rays the egg and sperm-cells of carefully pedigreed Onagra biennis at various p eriods of their development, both hef ore and during fertil­ization. Plants gro,vn from the seeds produced under this influence varied profoundly from their parents. Old characters disappeared, and new ones became evident. The treatment follo,ved by heritable alterations was one in which the pol­len grains were exposed for t,venty-four hours to rays from radium of 1,500,000 activity, con­tained in a sealed glass tube. Thus only the X-rays and possibly the more penetrating of the Beta-rays were effective. The three individuals with thick, leathery leaves, which resulted from this treatm~nt of the pollen, have already pro­duced a second generation in which the ne,v char­acters are seen to be reproduced, and, while a,vait­ing the continuance of this work, it may be as­sumed with fair certainty that the atypic strain will continue its development parallel to the pa­rental one.

Other striking departures in ontogeny were secured by exposure of the pollen and the ovary before and after fertilization, and also by treat­ment of maturing seeds, ,vhich ,vere not transmis­sible. Some slight modification of the technique might ,vell secure more extensive results and also permit an analysis of the difference, if any, be­tween son1atogenic and oogenic inductions and also illuminate the matter of the appearance of bud-sports.

OF ENVIRON1\1ENT 131

EFFECT OF SOLUTIONS ON GER~i-PLASM

The idea that solutions of various kinds might be introduced into the plant, and that modifica­tions of the ontogenetic procedure might be thus brought about, has been in the 1ninds of many workers in the laboratory. Developing inflor­escences have been excised and set in vessels con­taining salt solutions, and in other cases sub­stances were applied to cut surf aces of the vege­tative parts of the reproductive organs without result.

This in part was suggested to Darwin by vege­table galls, and in the first chapter of the Origin of Species (page 7) we find him saying:-

" Such facts as the complex and extraordinary out­growths which invariably follow from the insertion of a minute drop of poison by a gall-producing insect, show us what singular modification might result in the case of plants from a chemical change in the nature of the sap."

That his interest in this matter ,vas continued is evidenced by the following from Life and L etters:-

"Shortly before his death, my father began to experimentise on the possibility of producing galls arti­ficially. A letter to Sir J. D. }-looker (Nove1nber 3, 1880) shows the interest he felt in the question:-

"' I was delighted with Paget's Essay.1 ][ hear

• Disease in Pla11ts, by Sir James Paget. Garde11ers' Olii·o11icle, 1880.

132 THE DIRECT INFLUENCE

that he has occasionalJy attended to this subject from his youth. . . . I am very glad he has called attention to gaJJs: this has always seemed to me a profoundly in­teresting subject; and if I had been youno-er would take • b 1t up.'

" His interest in this subject was connected with his ever-present wish to learn something of the causes of variation. He imagined to himself wonderful galls caused to appear on the ovaries of plants, and by these means he thought it possible that the seed might be influenced, and thus new varieties arise. He made a considerable number of experiments by injecting various reagents into the tissues of leaves, and with some slight indications of success." '

In response to a request for a more detailed account of ,vork that may have been done on this subject by the elder Darwin, Professor Francis Darwin "''rites under date of November 27, 1908:-

" I am sorry that I can give you no further informa­tion about the experiments on gaIIs. lVly recollection is that we tried only injections with leaves and stems, and that no actual experiments were made on ovaries. I have never looked at his notes and do not know where they are at this moment, but I feel pretty sure that no definite 1·esults were obtained. I think acetic or formic acid was used in the experiments."

In the course of my extensive cultures dealing ,vith mutations, the theoretical conclusions of De Vries as to the pre-mutation period came up for serious consideration, and in order to obtain some evidence upon this point, as well as to test the assumption that the actual changes upon

'Life and L etters of Chcirles Danvin, by F. Darn~n, II, p. $17, 1905. New York.

D D

T

PLATE JI.

T. T. Up1ler nod lower asJ)eets or roe.cue of <E11otlura bictrn1a. D. 1>. lfo!lelte of dtri\'ati\'e resulting from ova.rial trctumcnt wilh zinc fmlpbate.

OF ENVIRONMENT 133

,vhich mutation rests ensue previous to the reduc­tion divisions leading to the formation of the reproductive nuclei, some ne,v methods of experi­mentation were developed. Among other opera­tions, solutions of sugar, calcium, potassium, and zinc ,vere injected by the use of hypodermic syringes into the developing ovaries of Raiman­nia, one of the evening primroses, early in 1905, with the result that out of the several hundreds of seeds borne by the treated ovaries sixteen in­dividuals were found to be notably atypic, among other characters: lacking the trichomes which are so conspicuous ,vith the parental form. T hese reproduced themselves in the second and third generations, coming true to t he newly assumed characters.

The same method was tried ,vith Oenothera biennis (Plate II), the common evening prim­rose of waste lands in eastern United States, ,vith the result that two individuals were found among the seedlings ,vhich ,vere different from the par­ents in a series of characters so distributed through the ontogenetic period that the deriva­tives 1 could be recognized by the first t,vo leaves, while the cotyledons were still ,vaxing. This form is no,v being cultivated at the Desert Lab-01·atory in the fifth generation, and is being thrown against the climatic selective factors in the mountain plantations at various altitudes.

'The deri~atives, lettered D in Plate II, are to be compared with the typical young plants, lettered T.

134 THE DIRECT INFLUENCE

T hese two successes had been scored by the use of crude instrwnents, entire lack of information

Schematic section of ovule showing action of reagent, intro­duced into ova.ry. m-i, micropylc, P, egg, a, antipodal nuclei, ;, inner integument. The reagent is taken up by the micropylar cells, and also follows the stream of nutritive material around the inner integument to the oeighborhood of the antipodal cells.

OF ENVIRONl\,IENT 135

as to the mechanical action of the reagents, and ,vith plants offe1·ing an ovarial structure most difficult to deal with. I n the development of the method, non-corrosive syringes of glass ,vith gold needles and an extended list of substances were employed, while a selection of species was made in ,vhich the reagents could be brought into con­tact ,vith the egg apparatus ·with proportionately least damage to its somatic structures. The sub­stitution of dyes for the substances to be used was found usefu[ in making out the mechanical results of an injection. Since these operations inevitably resulted in the destruction of a large number of ovules, it was found most convenient to work ,vith f 01·ms which are characterized by many-seeded ovaries. By this development of technique, more important results capable of def­inite analysis were secured and a fair basis for a theoretical explanation gained.

Many progenies representing genera in widely separated families are now under observation, but announcement of results beyond those of a year ago will be confined to Penstemon.

Penstemon wrightii is a species well marked and readily separable from its nearest relatives, which alone of the genus inhabits the slopes around the Desert Laboratory. It is, therefore, gro,ving under perfectly undisturbed conditi,ons. Various injections of zinc, calcium, and iodine into the young ovaries were made ,vhen these structures were not more than 3 mm. long and

136 THE DIRECT INFLUENCE

two-thirds of that diameter. A large number of the ovaries were killed by this treatment, but many matured. The percentage of germination in the species has been found to be low, however, and of the few hundreds of seeds sown, not more than a fifth germinated, and a fe"v were killed by drought. Eighty individuals grew to make ma­ture rosettes during 1908. Sixty of these pro­gressed so far as to bloom during the season, and of these, t,venty offered such material departures from the parental form as to be readily distin­guishable by visitors who had not critically ex­amined any member of the genus, or, indeed, had but little knowledge of plants. These twenty derivatives sho,ved eight distinct types, one of "\\1hich "vas represented by five individuals, one by four, t'~vo by three, one by two, and three by one. One type resulted from treatments with iodine, calcium, and zinc; four types came from a treat­ment of two reagents, two from iodine alone, and two from calcium alone. The revolution of the corona segments, the absence of the stiff clump of trichomes from the lower lip, increase in vis­cidity, mottling of the flower, and adhesion of leaf bases resulting in perfoliation, are some of the distinguishing marks of the ne,v forms. Of these characters some are already displayed by other members of the genus, while some of the progres­sive and retrogressive changes see1n to be taken before any relative had moved in the san1e direc­tion. . .. ·- . ,

OF ENVIRONMENT 137

Briefly summarizing the results of the investi­gations cited it may be taken as safely established that individually acquired or induced characters or modifications of existing qualities may be transmitted from one generation to another prac­tically unchanged. The assumption that organ­isms may make direct fitting or adaptive re~ spouses of the soma to environn1ental factors, ,vhich may be impressed on the germ-plasm and transmitted to successive generations, has not been confirmed by actual observation or experi­mental tests.

This tentative conclusion that somatogenic eharacters are not transmitted is one with which the following facts must always be taken into account: A-the physiological mechanism of or­ganisms, particularly of the seed-plants, is one which offers direct means of communication be­tween the soma and the germ-plasm in the form o1f reproductive elements, and ,vhich might per­mit the making of enduring impressions on embryonic tissues during ontogeny, or their effective communication to the egg, or sperm; B-the experimental and cult111·al test of the effect of repetition of the action of external agen­cies upon the soma in inducing hereditary .alter­ation has not yet been seriously attempted, and may indeed include the crucial requisite of the whole matter; C-a great number of structures and functions sustain the closest adaptive relation to environic forces, and important correlations

138 THE DIRECT INFLUENCE

are found among or between organs in a manner difficult of explanation upon any ground except that of simultaneous somatogenic induction.

!lfECHANISM'. OF THE INHERITED CHANGE

The modification of heredity brought about by the direct action of various agencies upon the germ-plasm is now safely established, and the available 1·esults are sufficient to justify some few generalizations as to the mechanism of the change. The most important evidence as to the nature of the disturbances which may ensue in reproductive elements comes from the ,vork of Gager, ~rho found that the action of radium might eliminate definite chromatin elements dur­ing the mitoses of the egg and pollen, and, fur­thermore, that some of the eggs fertilized by pollen subjected to such irradiation produced a progeny in which qualities different from those of the parental strain were exhibited. I t is not proven, of course, that the atypic strain was de­rived from a fertilization into ,vhich one less or one more chromosome entered, and possible dis­turbances of the autolytic action of the cell might ,vell be as important as the departures from nor­mal nutotic procedure. The ,vell-kno,vn influ­ence of temperatures upon these processes and also the readiness ,vith which unusual substances might be thrown into the cytoplasm in the ordi­nary course of nutrition, suggests tha.t the plant

OF ENVIRONl\ilENT 139

,vould be susceptible to modification in the stage between the reduction divisions and fertilization.

This conclusion is borne out by my own results in ,vhich solutions ,vere introduced into the ovary during this stage. The extent of the treatments, together " 'ith the diversity of results, makes pos­sible an analysis of other features. Thus the in­duction of more than one form by the use of a single reagent suggests either that different chro­matin elements ,vere affected in the separate ovular reactions, or that unlike parts of the chains of catalytic action ,vere interrupted or disturbed by the introduced substances. Some of the com­pounds used are inimical to enzymatic action, or may be capable of a negatively catalytic effect, 01· might indeed set up unusual splitting proc­esses, a state of affairs distinctly f avorable t o the last named alternative.

Not only 1nay irradiation and the introduction 0£ unusual substances occur naturally to the mod­ification of heredity in plants, but the climatic factors may, as in To,ver's experiments, exercise an influence upon the reaction velocities of va­rious parts of the metabolic series, or by varia­tions in humidity, regulate the excretion or 1l'eten­tion of active substances. All of these possibi]jties must be taken into account in attempts at expla­nation of bud-sports or bud-mutations in plants. It is to be seen that either egg or sperm may be affected by experin1ental agencies, and that the results do not differ in quality or degree. Gager's

140 THE DIRECT INFLUENCE

atypic forms were obtained by the treatment of pollen; my own from ovarial injections ,vhich might have acted upon the egg, or sperm, and T o"ver's work was ,vith both.

The new forms of beetles and plants which have thus been called into existence sustain the following general relations to their environ­ment and to the strains from ,vhich they ,vere derived:

1. Some of the species dealt with we1re gro,ving in the open, and dornesticated forms ,vere not in­cluded in t he experiments.

2. T he ne,vly arisen or modified characters maintained their distinctive appearance when crossed with the parental strains; in some no re­versions have yet been sbo,vn.

3. Discontinuous departures induced by ova­rial treatments in plants ,vere full and constant within the limits of fluctuability with the first generation. Similar abruptness of divergence is exhibited by beetles in some cases, ,vhile in others more than one generation, after removal from experimental conditions, v,as necessary to secure full expression.

4. lVlany aberrations induced by irradiation in plants and by climatic effects in beetles ,vere of the nature of closely continuous variations, the range of which ,vas widened by the exciting agent. Some of the derivati,res of P enstemon may prove to be of this character. The single derivative of Oenothera biennis obtained by ova-

OJF ENVIRON1"1ENT 141

rial treatment ,vith zinc sulphate is distinctly discontinuous ,vith the parent.

5. Some of the modifications may be regarded as an increase of capacities already present; some imply the loss of characters or structures, and some are acquisitions; in more than one instance qualities ne,v to the genus have been taken on. Changes such as the mottling of a solidly col­o:red flower 1nay be regarded as a loss of a por­tion of a design, the total effect of which was a shaded or a self color, or it may be taken as a diifferentiation in advance.

6. The behavior of the ne·wly derived forms ,vhen subjected to natural conditions, competi­tion, and possibility of hybridization ,vith paren­tal forms, has been extremely diverse. Some of the beetles have been swamped by hybridization ,\rith the parental form; others have displayed· some power of endurance. The plant deriva­tives induced by ovarial treatments were weaker than the parent in some localities, and more en­during in others. The derivative of Oenothera biennis induced by a zinc sulphate ovarial treat­n1ent is less adapted to xerophytic conditions than the parent, does not readily hybridize with it ,vhen gro"\-vn in contact, and its earlier char­acters appear to be dominant ,vhen crosses are made artificially.

7. The departures obtained by the experi­mental manipulation of exte1·nal exciting agen­cies bear a general similarity to the initiatory

142 THE I NFLUENCE OF ENVIRONMENT

and modificational phenomena exhibited by or­ganisms in a state of nature, and it seems justi­fiable to conclude that the processes disturbed or set in motion are identi-cal ·with some of those concerned in the main evolutionary development of organisms.

THE BEHA VIOR OF UNIT CHARAC­TERS IN HEREDITY

BY

W. E. CASTLE

No ONE recognizes more frankly and joyously than ·would Dar,vin, were he here to-day, the great advance which has been made in our knowl­edge of heredity since his time. H is work and writings have po1nted the way to that advance, and it is largely owing to a return to the experi­mental method of testing hypotheses, which Dar­,vin used so successfully, that the remarkable progress of the last decade has been made pos­sible. We do, therefore, the greatest honor to Darwin if ,ve pause to consider what superstruc­ture of knowledge has been built on the f ounda­tions which he laid. This superstructure is, in­deed, still in the building, and it is not easy in all cases to distinguish between the solid st1ucture of proved fact :and the scaffolding of hypothesis. Still, the attempt should be made, and it will give us encouragement to discover that, notwith­standing the considerable amount of rubbish lying about, there is, neve1-theless, good con­structive work going on here which gives prom­ise of permanency.

143

144 THE BEHAVIOR OF UNIT

The particular topic Vl7hich I have been asked to discuss is the behavior of unit characters in heredity.

The subject of heredity units is one to which Darwin gave much thought. With cha1·acteristic thoroughness and patience he assembled the facts of inheritance, reversion, bud variation, regenera­tion, and related subjects, which in his opinion had a con1mon underlying cause, and with delib­eration framed a tentative hypothesis to explain them. This hypothesis, which he called pangen­esis, was itself short-lived, but has left a numer­ous progeny. The most important are the idio­plasm theories of W eismann and Nageli, and the theory of intracellular pangenesis of De Vries. Dar·win's hypothesis was useful because it set people to thinking, observing, and experiment­ing. The theories of W eismann, Niigeli, and De Vries were attempts to bring Dar,vin's fun­damental idea into harmony ·with facts subse­quently discovered. All these theories V11ere scaffolding, not masonry.

MENDEL'S LAW

A conception of unit characters fundamen­tally different from Dar,vin's, one which antedates slightly the pangenesis theory, but which suffered total eclipse by it, is to-day kno,vn as Mendel's law_ It accords so fully ,vith a variety of biological facts discovered

CHARACT ERS I N HEREDITY 145

since Dar,vin's time, that we are coming to re­gard it as the cornerstone of our kno,vledge of heredity.

The romantic story of Gregor Mendel is known to you, ho,v toiling long years in obscurity hybridizing garden-peas, he made a great dis­covery only to see it scarce noticed and soon forgotten. He himself, mean"\vhile, called to ad­minister the affairs of an ecclesiastical establish­ment, ,vas forced to relinquish his f avorite pur­suit of scientific investigation, and ,vas thus unable to follow up his great discovery and force it upon the attention of scientists. So he died unhonored by his fellow-scientists and all but unkno,vn to them.

The story of how, a generation later, Mendel's law was rediscovered thrice over is scarcely less romantic. That the rediscoverers, having first established the law independently and then hav­ing discovered Mendel, should assign the honor unreservedly to ithe obscure and forgotten Abbot of Briinn, is a circumstance ,vhich should cause us long to remember and honor the names of De Vries, Correns, .and Tschermak.

According to D arwin's pangenesis theory, the reproductive cell is made up of minute units de­rived from and representing each part or organ of the entire body. A f e\v critical experiments instituted by Galton sho,ved this theory to be untenable, and they seem to have involved in public esteem an adverse decision against all less

146 THE BEHAVIOR OF UNIT

well-known theories in which the existence of units in heredity was assumed. Such was the fate deservedly of the highly speculative theories of Niigeli, and undeservedly of the generalization reached by Gregor i1endel, a scientific protege of Niigeli.

l\'(endel did not frame any complete theory of heredity, but observed, as the result of experi­ment, that certain characters of plants are, in crosses, inherited by definite proportions of the off spring. He framed in general terms a state­ment of what those proportions are and advanced a simple hypothesis to accow1t for them. Men­del's generalization we kno",r to-day as Mendel's law, and his hypothesis as the theory of unit characters.

By a unit character in the sense of Mendel's law, we mean any quality or part of an organism, or assemblage of qualities or parts, ,vhich can be shown to be transmitted in heredity as a whole and independently of other qualities or parts. Thus i1endel found that the starchy char­acter of the seed of some varieties of garden­peas, which makes the seeds round and smooth when dried, is a quality which may by suitable crosses be replaced by a sugary character, causing wrinkling of the seed on drying. This change of the seed character through crossing may be brought about without essential modification of the other parts of the plant. R ound and ·wrin­kled seed forms in peas, l\1endel accordingly con-

CHARACTERS IN HEREDITY 147

sidered to be alternative and interchangeable unit characters.

Similarly yello,v color of the cotyledons in the seed of peas ,vas found to be a unit character alternative ,vith green color. In animals ,ve find similar simple unit characters to e:,.,.-ist. Thus in mammals black pigmentation is due to the pres­ence of a unit c:haracter which may be replaced by another changing the pigmentation to brown. Among horned ruminants, such as cattle and sheep, development of the horns depends upon the presence of a unit character which may be replaced by ( or perhaps become associated with) another, in the presence of which horns fail to develop.

RECENT EXTENSIONS OF THE THEORY OF HEREDITARY UNITS

In cases less simple than these, a unit character m.ay have more than a single manifestation, as where a plant having flowers of a certain color has also a similar but f ainte1· col oration oif the stem, or a mammal with black hair-pigment has also black skin-pigment, while one ,vith brown hair-pigment has also bro,vn skin-pigment. In still other cases, two or more independent unit characters must be present together to produce a single visible effect. This fact was unkno,vn to Mendel. Its discovery constitutes one of the most recent and important advances made in our

148 THE BEHAVI OR OF UNIT

knowledge of heredity, and merits further con­sideration.

Mendel conceived of unit characters as exist­ing ahvays in pairs, one of which might be sub­stituted for the other by suitable crosses. We are now coming to realize that this is an inade­quate staten1ent of the matter. , i\That is paired is not the unit character alone, but the entire or­ganism. All its characters and parts have their basis in paired structures in the protoplasm of the individual, one member of each pair being derived from the motheir of the individual, one from the father. The cytologist has visible evi­dence of this fact in the doubling of the number of chromosomes at fertilization, and their subse­quent reduction when the reproductive cells ripen; the experimental breeder has e·vidence of this duality equally convincing as regards many hereditary characters, but the evidence is clearest in the case of characters '\-Vhich occasionally are lost. It is only in such cases that we can ,vith certainty identify unit characters. By compar­ing an individual which has a certain character with another individual which does not have it, ,ve learn how much that character includes, and we can learn this in no other ,vay. Experimen­tal breeding ,vill show '\-vhether the character is simple, is really a unit, or is an aggregate of in­dependent units. Thus if we cross a black guinea-pig with one which lacks black-say a. brown one-we obtain only black off spring, but

CHARACTERS IN HEREDITY 149

these bred inter se produce both black off spring and bro,vn ones., in the proportion three black to one brown. vVe thus learn that black is a unit character. It ,vas contributed by one par­ent to the cross, but not by the other, and t1·ans­miitted by the cross-bred individual to half its off spring, but not to the other half. This is M endel's explanation of the 8:1 ratio, now fa­miliar to every biologist.

But if we cross the same black parent in the fore going case, not ,vith a bro,vn individual, but with a white one or with a yello,v one, we may obtain not black offspring, but ,vild-colored " agouti " ones, ,vhich bred inter se will produce agouti, black, white ( or else yello,v) young, ,vith perhaps those of other ne,v classes in addition. Such a result as this puzzled D ar,vin, and would naturally puzzle any one, but in the light of Men­del's la,v becomes capable of 1·eady explanation. The production of black pigment is a process in which more than one unit character is concerned; the production of a gray coat involves more units still; ho,v many, can in part be determined by a study of the number of classes of individuals occurring in the second generation from the cross, and the numerical proportions in ,vhich the individuals occur in these classes. The point may be made clearer by fallowing through a particular case, to ,vhich Dar,vin makes reference.

150 THE BEHA VIOR OF UNIT

Primary color-varicties of rabbits Constitutcnt factors

u I

Gray ............................. A-C--B-E

Black ........................... .

I I

u I C--B-E I I

u I

Yellow . . . . . . . . . . . . . . . . . ........... A-C--B-R

Sooty . . . . ....................... .

I I

u I C--B-R I I

If rabbjts of various colors are turned loose together in a warren, the population is likely to revert more or less completely to the gray color­ation of wild rabbits. The foregoing is in sub­stance the statement of Darwin; and its correct­ness is fully established.

THE FACTOR HYPOTHESIS IN RABBIT BREEDING

Before going further it n1ay be ,vell to describe the color varieties of rabbits. These are exceed-

CHARACTERS IN HEREDITY 151

ingly numerous, but for otll" purpose may be reduced to four fundamental color types in addi­tion to the albino or uncolored type. These four are gray, bl11ck, yello,v, and sooty yellov;. The last I shall for simplicity call sooty. Gray is the original or ,vild type from ,vhich the others have been derived. The gray fur contains both black and yello,v pigments, but so disposed as to pro­duce a pattern on the individual hair, viz., a dark base and tip and in bet,veen them a band of yel­low. The lo,ver surfaces of the body also are ,vhjtish. In the black variety the hair pattern is wanting, and the black pig1nent occurs through­out the length of each hair and all over the body. In the yellow variety black pigment is largely wanting throughout the coat, though present in the eye and, in very small quantities, in the hair. The presence of the hair-pattern is nevertheless suggested by ·whitish under surfaces, as in the gray type. The sooty type closely resembles the yellow, but has colored under surf aces, instead of white ones. Yellow and sooty correspond with gray and black 1·espectively, but ,vith a greatly reduced amount of black pigment in the fur, so that yello,v predominates there.

Let us no,v consider the relation of these four types one to the other. Gray crossed ,vith any other type produces only gray offspring. Black crossed with yellow produces gray, but crossed with sooty produces black. Y eMow crossed with sooty produces only yello,v. Sooty disappears

15~ THE BEHA VIOR OF UNIT

in crosses with any other type; it is recessive in the Mendelian sense ,vith reference to all the others.

Darwin explained the reversion of feral rab­bits to the gray type on t,vo grounds: (I) " a tendency in all crossed animals to revert to their primordial state," and (2) the action of a more " natural " environment ,vhen the animals are free than when they are in captivity. In reality neither of these conjectured reasons has anything to do ·with the case. Some varieties ,vill under no circumstances give reversion, if crossed ,vith each other; but reversion may be obtained as readily in captivity as any,vhere. Reversion is due solely to the bringing together of certain. unit char­acters, ,vhose joint action is necessary to produce the observed result.

In producing the gray coat characteristic of ,vild rabbits at least eight independent unit char­acters are involved. Other color varieties of the rabbit have arisen by regressive variation, i.e. by loss, more or less complete, of one or more of these unit characters.

To illustrate the m.atter, let us consider the result of a particular experiment. Black rab­bits were crossed ,vith light yello,v ( cream) ones, and produced ·wild-colored gray offspring. These bred inter se produced young of a variety of colors, but among them grays again predom­inated. All the first generation grays seemed to breed alike, producing young of various colors,

CHARACTERS IN HEREDITY 158

but not so those of the second generation ( F 2) • Among these thirty-t\vo different classes may be recognized, that is, thirty-two sorts which, though all .looking alike, produce each a different assort­ment of young. These assortments are:-

1. Gray only. ~- Gray, and black. 8. Gray, and white. 4. Gray, black, and white. 5. Gray, and yellow. 6. Gray, black, yellow, and sooty. 7. Gray, yellow, and white. 8. Gray, black, yellow, sooty, and white.

Eight other varieties produce the same sorts of young as these eight respectively, but in addition produce dilute pigmented ones of the same color types, i.e. blue-grays as ,vell as grays, blue as " 'ell as black, cream as ,vell as yellow, and pale sooty as well as sooty. Sixteen other varieties produce the same assortments of young as these sixteen, but in addition produce animals spotted " 'ith ,vhite in each of the several color types.

The facts briefly stated are now before us. We can distinguish among the second generatioa gray rabbits thirty-two different kinds, all look­ing alike but all breeding differently. Out of this apparent chaos the Iv[endelian theory of unit characters brings law and order; no other ex­planation has been offered which makes anything but chaos out of the situation. The numbe1· of distinguishable classes, thirty-t"·o, sho,vs that

154 THE BEHAVIOR OF UNIT

five independently variable characters are in­volved; the proportions in which the several sorts of young are produced by each class of gray parent confirms this conclusion. If the number of independent unit characters concerned were one greater, as it is in guinea-pigs, the total num­ber of classes of parents would be doubled to sixty-four; if it were one less, the number of classes of parents ,vould be reduced one-half, to sixteen.

W hat now are the five variable unit characters concerned in producing the gray coat of a rab­bit and ,:vhat are their relations one to another? I n ans,vering this question it will be necessary to mention a sixth unit character ·which contrib­utes to the result, though not itself variable. It will be convenient also to designate each sep­arate unit character by a letter or symbol. The six unit characters to which reference has been made are:-

1. C, a general color factor, something necessary to the production of all pigment, wanting only in albinos.

~- B, a factor fol· black, some substance, which acting upon C, produces black pigment; this is in rabbits an unvarying factor, though in other mammals it is often variable.

The four remaining factors modify t he action of one or the other of these two; they are :-

3. A, a pattern-factor governing the distribution of black on the individual hair, so that it converts black into gray, blue into blue-gray, and sooty into yellow.

._.

CHARACTERS I N HEREDITY 155

4. E, a factor governing the extension of black over the body generally ; in its most extended distribution, black occurs on all hairs of the body, in its most restricted distribution (R) it scarcely extends beyond the eye, and the skin of the extremities, the hair being practically devoid of black pigment and appearing yel­low; that this factor is distinct from B, is shown by the fact that it can, in guinea-pigs, be dissociated from B and beC'ome associated with brown pigmentation.

5. U, a factor· goYerning the distribution of C over the body; if C covers the whole body ( condition U), the whole body is pigmented; if C covers part of the coat only ( condition S), the rest is occupied by spots of white. That this unit is distinct .from C is shown by the fact that it is transmissible th1·ough animals which lack C, that is, through albinos.

6. I, a factot· go,rei•ning the intensity of the pig­mentation. It is a modifier of C, for it affects all pig­ments alike, yellow and brown as well as black, all of which pigments have their common basis in C; but I is distinct from C, fo1· it is transmissible through albinos, which lack C. When I is present all the pigments are intense; when I is absent, or rather weakened to the condition D, the piigmentation is dilute, as in blue and cream, the dilute conditions of black and yellow respectively.

It is clear from ,vhat has just been said that these various factors, though separately variable, are not entirely inc;lependent of each other. Some produce no visible effects unless others are pres­ent. Thus if C alone is wanting, none of the others is visible. To aid in expressing the inter­relationship of the factors I think it useful to imitate the organic chemist and employ dia­grams. Thus a diagram might be constructed as follo"·s to express the relations of the six factors

156 THE BEHA VIOR OF UNIT

in a reproductive cell transmitting the color char­acters of a gray rabbit:-

U I

A-C-B-E I [

It is possible that in protoplasm ,ve have or­ganic molecules built up in some such way, and that regressive variations arise by dropping off the constituent parts of the molecule one by one. Certainly it is loss or extreme modification of factors that produces the ordinary ,col or varia­tions. If ..t\ drops out, ,ve have a black rabbit instead of a gray; if E is replaced by R, a yello,v one is produced; if both these changes occur, a sooty one; if U is replaced by S, ,ve have a spotted gray rabbit; if both U is replaced by S, and A is lost, a spotted black rabbit results: if C is lost,. ,ve have an albino, ·whose breeding ca­pacity varies with the number of other invisible factors which remain.

The list of kno·wn color factors is not ex­hausted by those which I have enumerated. One other, a factor for brown pigmentation, Br, has been revealed in the case of the guinea-pig, the mouse, and the dog, by loss of factor B. Bro,vn pigmentation then everywhere replaces black. This factor bears the same relation as does B to both C and E. Some time doubtless we shall see

CH.ARACTERS IN HEREDITY 157

bro,vn and cinnamon-gray rabbits produced by the same mutation, loss of factor B, ,vhich has produced bro"'n and cinnamon-agouti varieties among mice and guinea-pigs. Again there must be in all rodents a factor Y wlhich, acting in the presence of C, produces yellow pigment, but Y has not unmistakably revealed itself by getting lost. It is ahvays present, if C is, and may rep­resent possibly a step on the road to the produc­tion of black and bro,vn. Certainly, however, its distribution on the body of the rabbit is inde­pendent of the factor E, though subject to U. In the diagram, therefore, Y and Br ,vill prob­ably fall into the positions shown here\vith for the guinea-pig:-

U B

I / "-.. A-C-Y E

I "/ I Br

This diagram ,vould express the interrelations of the color factors, as ,ve no,v understand the matter, in a reproductive cell or gamete trans­mitting the ,vild type of coat. But sucl1 a gamete might be formed by some sixty-four dif­ferent kinds of ,vild-coated individuals. The only differences, ho"vever, bet·ween these sixty­four kinds of individuals "vould lie in ,vhether they contained a single or a double dose of each of the factors enumerated. I therefore propose

158 TfIE BEHAVI OR OF UNI'!'

fu1·ther to imitate the organic chemist by placing a subscript, 2, after each factor doubly represented in the indiYidual, i.e. after every factor in ,vhich the individual is homozygous, ,vhile else,vhere omitting it. ,v e shall thus haYe a zygotic for­mula which will look like a chemical formula, and which will serve the same useful purpose of ex­pressing many facts clearly and in small com­pass.

The zygotic formula of the pure gray rabbit ·will then be B2 E2 A2 C2 12 U2; the gray rabbit which also gives black young ·will be single in A, but otherwise identical in forinula ,vith the fore­going, viz., B2 E2 A C2 12 U 2, and so on through the list.

The question ·will naturally suggest itself, how common are unit characters? Are all the quali­t ies and parts of organisms due to them, or only certain kinds of qualities or parts? Such ques­tions can not at present be ans,vered satisfac­torily. I t may be pointed out, ho,vever, that ,ve are already acquainted ,vith a considerable Ya­riety of Mendelizing characters. These include in plants both structural and physiological char­acters of stem, leaf, flo·wer, and seed. I n ani­mals, ·where a less extensive study has as yet been made and \vhere the organization is much 1nore complex, the unit characters thus f a1· identified relate chiefly to superficial characters, pigmenta­tion, hair-structure, and the like. Certain pecu­liar variations of the skeleton, digital variations,

CHARACTERS IN H EREDITY 159

and the like, have, ho\vever, been sho,vn to l\fen­delize, and further study ,vill undoubtedly reveal the existence of additional unit characters. We should also bear in 1nind that \\'e have no means of identifying unit characters except as they drop out of existence in certain individuals. l\fany unit characters are probably of such vital impor­tance to the organism that they cannot be dis­pensed with, for when they are lost the organism ceases to exist. In such cases the existence of unit characters, ho,vever probable, can not be unmistakably demonstrated by any method now kno"vn to us. Fragmentary as our present kno,vledge is, it is doubtful whether any category of organs, quantities, or parts can be mentioned ,vhlch is not subject to l\1endelian inheritance. If we could only discover some means of sup­pressing particular unit characters, what an in­strument for unraveling the mysteries of inheri­tance would be ours!

Time does not suffice to discuss the mutability or immutability of the unit characters, the pos­sibility of ne,v characters arising de nova, and other interesting but disputed questions. These are matters ,vith ,vhich the second fifty years after Dar,vin ,vill have to deal.

MUTATION

BY

CHARLES B. DAVEN PORT

FORTY-THREE years after the Ori,gin of Spe­cies there appeared the first part of a book by the D utch naturalist, H ugo de Vries, entitled Die M utationstheorie. 1\1any other theories of evo­lution have been propounded and defended in the last half-century, but hardly any other has commanded such immediate consideration and received such widespread acceptance. The muta­tion t heory must therefore contain certain evi­dent elements of truth. L et us consider its scope and some of the evidence on which it rests.

!\1UTATION DEFINED

First of all it is necessary to define mutation in D e Vries' sense and to show its relation to other evolutionary principles. Mutation in any strain is a change in the unhybridized germ­plasm of that strain which is characterized by the acquisition or loss of one or more unit charac­ters. There has already been presented to you the evidence for unit characters, a conception first clearly elucidated by Darwin. I think it may fairly be said that the mutation theory rests on the doctrine of unit characters and applies

160 .

MUTATI ON 161

only so far as that doctrine applies. As even the most extreme neo-D arwinian school recognizes such units with their representatives ( determin­ants of Weismann) in the egg, and as in evolu­tion there must be the acquisition or loss of at least some one character, it might be expected that the idea of mutation as defined above ,vould find universal acceptance. But it has not done so. The difference of opinion relates to the gra­dient of the transition by ·which a new unit char­acter is introduced or an old one disappears. l\f utation in D e Vries' sense implies the sudden appearance, complete in the first generation, of the ne,v unit character and its germinal repre­sentative, the pangene or determinant. Muta­tion is regarded by many who call themselves D ar,vinians as an innovation and as opposed to Dar,vin's fundamental assumptions. F or the neo-D ar,vinian conceives the determinant as gradually changing in evolution and exhibiting in the adult forms of successive generations the same continuous series that an organ shows in its ontogenetic development. The vie,v of neo­D arwinians is ,vell indicated in the following quotation from W eismann 1

:-

" If I mistake not w @ may say at least so much that all varia t ions a re, in ul t imate instances, quantitative, and that they depend on the increase or decrease of the vital pai-ticles, or their constituents, the molecules. . . . What appears to us a qualita tive variation is, in reality, not hing more than a greater or less, a different mingling of the constituents which make up a higher unit, an

' The Evolution Theory, Vol .. II, p. 161.

16~ MUTATION

unequal (nc1·case or decrease of these constituents, the lower units. \,Ve speak of the simple o-rowth of a cell when its mass increases without any ~Iteration in its composition . . . but the cell changes its constitution when this pl·oportion is disturbed, when, for instance, the red pigment granules w·hich were formerly present but scarcely visible increase so that the cell looks red. If there had previously been no red granules present, they might have arisen through the breaking up of certain particles-of protoplasm, for instance,-in the course of metabolism so that, among other substances, red granules of uric acid or some other red stuff were pro­duced. In this case, also, the qualitative change would depend on an increase or decrease of certain simpler molecules and atoms constituting the protoplasm-mole­cule. Thus, in ultimate instance, all variations depend upon quantitative changes of the constituents of which the varying part is composed."

So far W eismann. vVith his accustomed thor­oughness he has f ollo,ved the consequences of his stand that quantitative changes alone are suf­ficient to account for the processes of evolution, although to do so he has been forced to take the position that the loss of certain atoms from a molecule is merely a quantitative change, and that the appearance of a new quality is quantita­tive because merely of the order of a change from zero to one! ,,r eismann's argument here degen­erates to a mere play of words. J ust as good an argument could be made to support the assertion that all changes are qualitative-that 96 is qual­itatively unlike 97. But if the ideas are both to be retained, then it must be admitt ed that a loss of aton1s from a molecule, the appearance of

~IUTATION 163

a new kind of molecule, the appearance of red pigment where none ,vas, a1·e all qualitative changes. ""r eismann's admission that red gran­ules may arise de novo in consequence of a molec­ular change in the germ-plasm is an admission that an organis1n may undergo a qualitative va­riation, and this is a mutation. Recalling; then, in recapitulation, that every character of an or­ganisn1 has a chemical basis, that a new character implies one or more ne,v kinds of molecules and that molecular change is essentially qualitative and discontinuous, the conclusion seems safe t hat variations involving ne,v characters are essen­tially discontinuous, and consequently of the order of mutations.

DAR,VINIAN VARIATIONS

At this time the ,v eismannian vie,v and that of the neo-D arwinists in general is of less interest than that of D a1·\vin himself. vVhat was D ar­win's attitude on the question whether variations that play a part in evolution are of the qualita­tive or the quantitative order? T he ans,ver seen1s to be simple; the question did not present itself to him- our formulation of the matter is a comparatively recent product of scientific anal­ysis. D arwin did recognize sa1tation as opposed to ordinary variability, and remarks: " I t is dif­ficult to drawn any distinct line between a vari­ati,on and a monstrosity." I n his V ariation of A nimals and P lants under Domestication, D ar-

164 MUTATI ON

win cites cases of characteristics that he believes to have arisen suddenly, such as the blackness of the japanned peacock, jaw appendages of pigs, short upper jaw and hornlessness in cattle, short­leggedness in sheep and dogs, elongated wool in merinos, and downless fruit in peaches. These instances sufficiently indicate Dar,vin's recogni­tion of saltation, and if he was led to reject it as the usual mode of modification of species, he did so because the doctrine had a crude form and car­ried ,vith it the connotation of something terato­logical or pathological. But is there sufficient evidence that, in rejecting saltation, he regarded evolutionary changes in unit characters to pro­ceed always by the fourth place of decimals? On the contrary, his examples of variations are very unlike the raw material of the biometric school. This is a sample of his idea of variation in poultry:-

" The tarsi are often feathered. The ieet in many breeds are furnished with addjtional toes. Golden spangled Polish fowls are said to have the skin between the toes well developed."

I n the short section labeled " Remarkable va­riations of Goats," Da1·win refers to the great ears of goats of the I sland of Mauritius, to the various f oTms of mammre, to throat appendages, hornlessness, and presence or absence of toe glands. The entire work on Variation under Domestication demonstrates that Dar,vin fre­quently, if not usually, meant by Variation the

MUTATION 165

acquisition or loss of unit char.acters. Darwin's position has been sadly misrepresented by those neo-Dar,vinians ,vho have insisted that Natural Selection operates only upon variations of the quantitative order. In the Origin of Species, Darwin ,vas arguing for continuity and natural law, and accepted the principle" natura non facit saltum" as in accord ,vith the new view. Con­tinuity in nature was his great a.rgument against creation. "Why," he asks, "should all the parts and organs of n1any independent beings, each supposed to have been separately created for its special place in nature, be so invariably linked together by gradated steps? " Fifty years .ago, we 1nust remember, it was the battle of continu­ity against special creation that was being fought and not the gradual as opposed to the sudden appearance of a unit character.

Recognizing, then, that the mutation theory, far from being opposed to Darwin's theory of the origin of species, ,vould have been welcomed by him, we pass with more satisfaction, on the occasion of this celebration, to a detailed consid­eration of some of the facts of mutation.

lV!UTATIONS IN NATURE

The classical case of mutation is that of the evening primrose, named after Lamarck, but henceforth to be no less closely linked ,vith the name of his evolutionary successor, De Vries.

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Here is a plant of characteristic form and flower ,vhich regularly produces a small percentage of offspring of strikingly different forms- sparsely branched instead of profusely, ,vith brittle leaves instead of smooth, of stunted size and small flo,v­ers, with strap-shaped or ,vith ovoidal leaYes in place of lanceolate. The unit characters that appear in these peculiar progeny of lamarclciana do not int ergrade with the corresponding charac­ters of the parents, and, on self-fertilization, are reproduced in successive generations.

While the particular kind of mutation exhib­ited by Lamarck's primrose is rare, it is common to find species in which an organ appears, in dif­ferent individuals, in a nu1nber of distinct forms constituting the so-called "elementary species" -a tern1 that seems justified since, bred to their like, these forms are reproduced in successive generations. Striking examples of this sort have been found in wild violets by Doctor Ezra Brain­erd, and in the shepherd's purse by D octors Lotsy and Shull. Animals have been less care­fully scrutinized for elen1entary species; but we are not without instances. The true bugs and the straight-winged insects often sho,v both long­winged and short-,vinged forn1s, ·without inter­grades. Some tiger beetles, of both sexes, appear either in a bro,vn or a blue-green dress. Wheeler has collected over a score of pink katydids discov­ered in the United States ·within recent years, and has noted cases of pink forms of green hemip-

l\IUTATION 167

tera. The same green species sometimes have a bro,vn form, too. In these cases the ne\.v char­acters of pinkness and of brownness have un­doubtedly arisen suddenly and no intergrades are known. Of the common J\{ay beetle, I am in­formed by Professor Forbes, no less than forty­t,vo forms are known from Illinois alone, several of them difficult to distinguish by superficial characters, all of then1 readily separated by Tef­erence to the copulatory structuTes, which are dif­ferent in the various species and in the two sexes. " These structures are so constant," writes Pro­fessor Forbes, " that one of my assistants who has handled over ten thousand specimens of one species for determination, says that they are all like castings from the same mold." There are features of this case that certainly look like mu­tation; particularly the large number of species in a small area separated by non-intergrading differences in one variable organ. But, as Pro­fessor Forbes suggests, there is one difficulty in the way of seeing how the differences could have arisen by mutation: the copulating organs in each species are mechanically adapted to each other; and this requires that a coincident and coadaptive mutation occur in the two sexes. But this is a true difficulty only so long as ,ve conceive the entire organ to be a single unit character. There is, ho,vever, as little reason for so conceiving it as for regarding the human hand as one unit character instead of many units. The evolu-

168 MUTATION

tion of mutually adapted sex organs may be readily conceived as follows: Let a new species differ from its ancestor by a character m; then, in accordance with the familiar fact of sex dimor­phism in unit characters this takes in the two sexes the forms m' and m". If the t\'to sex-forms are incompatible the new species will come to nought; but if not incompatible the t,\·o modi­fied sexes may interbreed and be prevented from breeding ,vith the parent species. By the addition of a series of new unit characters, n, o, p, etc.­each of ,vhich must stand the test of co1npatibility in the two sexes-a complex dimorphic organ may be built up by mutation. It were wearisome to attempt ito catalogue the mutant-like variations that have been recorded among insects and other animals. The great ,vork of Bateson, "Jtlaterials for the Study of Variation, is full of instances, and the entomological and conchological jour­nals are full of many more. Every·where ,ve find, along with the universal quantitative variation, cases of qualitative, discontinuous variation in­volving entire unit characters; and these new characters are, probably, judging froJin our expe­rience ,vith domesticated animals, inheritable.

fl'!UTATIONS UNDER DOl\!ESTICATION

When we study a group of domesticated or­ganisms, such as poultry, we find the races dis­tinguished by characters that do not intergrade

MUTATION 169

and can not be made to intergrade by crossing. An instance will show how these characters be­have. ,v-hen a black fowl is crossed with an albino, of the Silky race, the off spring are black ,vith a trace of red in the males. When the hy­brids are mated together they yield albinos, solid blacks, blacks marked with red, and typically colored red-and-black Games. If you keep on crossing together the red-ticked blacks you ahvays get albinos, solid blacks, red-ticked blacks and Games, and nothing else. Such an experi­ence makes clear, better than any argument, the meaning of unit character, discontinuity, and mu­tation. Further .analysis of this case shO'ws that the black fowl has a unit character-melanic super-pigmentation- that has been added to the primitive Game coloration; and the albino lacks a unit character- the pigment forming enzyme -found in the ancestral plumage. Neither of these unit characters blends in the crossing. If now these unit characters of normal plum.age color, excessive melanism, and albinism are to­day non-blending, essentially unalterable char­acters, it is probable that they have always been so :and were so in their origin. But we have direct evidence as to this matter. In discussing the case of the black-shouldered peacock, Darwin concludes: " The case is the most remarkable one ever recorded of the abrupt appearance of a new form." If the black peacock arose sud­denly, so probably did the first black Medite:rra-

170 MUTATION

nean fowl, at a time long before records were kept. Again ,ve find that human albinos appear suddenly, complete, and breed true like real spe­cies. W ,e have other cases of semi-albinos of which the history is known. The blue-green Australian parakeets were first brought to Eu­rope in 1831. I n 1872 an expert records seeing a single yello,v specimen, and by 1877 they had become relatively common in Germany, since they breed true, and now they may be found in most bird-stores of our cities. This yellow par­akeet has lost the power of forming black pig­ment, and the new chai-acter appeared suddenly and completely. There is every reason for be­lieving that the yellow canary was thus derived from the green canary, the white Java sparrow from the gray form, and the albino f o,vl from a pigmented ancestor. The sudden origin of color changes is generally admitted by breeders and field naturalists; and many more cases of sud­denly appearing characters nught be cited, such as hornlessness in cattle, sheep, and goats; tail­lessness in cats, dogs, and poultry; hairlessness in horses, cows, and dogs; spinelessness and hair­lessness in vegetative organs and fruits; fascia­tion of the stein and pelorism of the leaves and petals of many plants, and extra digits in poul­try, s,vine, horses, and man. These are examples, merely, for since man first began to domesticate plants and animals hundreds of new characters have appeared suddenly and completely and ea-

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pable of vigorous transmission. The frequency of such mutations depends on the nwnber of individuals studied.

No,v, during the past four years I have bred, handled, and described over ten thousand poul­try of known ancestry. Of striking ne,v char­acters I have observed 1nany, some incompatible ,vith normal existence; otheil:s in no ,vay unfit­ting the individual for continued life. In the egg, unhatched, I have obtained Siamese t~vins, anteriorly duplex individuals ,vith shortened upper ja,v (like that of the niata cattle, pug dogs, and some carp), and chicks ,vith thigh bones absent. T here have been reared chicks with toes gro,vn together by a ,veb, ,vithout toe­nail or ,vith t,vo toe-nails on one toe; ,vith five toes, six toes, seven toes, or three toes; ,vith one , 1ving lacking or both absant; '-\'ith t,vo pair of spurs; ,vithout oil-gland or tail ( though fro1n tailed ancestry) ; with neck nearly devoid of feathers; with cerebral hernia and a great crest; ,'lllth feather shaft curved; ,viith barbs t,visted and dicotomously branched, or lacking altogether. Of the co1nb alone I have a score off orms: single, double, triple, quintuple, and walnut, V-shaped, cup-shaped, comprising two horns or four or six, absent posteriorly, absent anteriorly, and absent altogether. All of these conditions have been offered me ,v:ithout the least effort or conscious selection on my part, and each appeared in the first generation as well developed peculiarities,

172 MUTATI ON

and in so far as their inheritance ,vas witnessed each refused to blend when mated with a dissim­ilar form. For example. the pea X single gives a pea comb ,vhich in the next generation yields sin­gle and pea; cerebral hernia and no hernia give no hernia in the first generation, but hernia again in the second ; taillessness may follo,v the Men­delian formula, polydactylism approaches it, and the color varieties illustrate it strikingly. I n a ,vord, ·while quantitative variations are never ab­sent in poultry, the sudden appearance and dis­appearance of full-fledged characters is most striking. Mutation as thus defined presents to the breedel' as a common phenomenon. .But, say the neo-Dar,vinists, your mutations are of a teratological sort and have nothing to do ,vith species as ,ve find them in nature. I n reply I admit, first, that under domestication many mu­tations are preserved by man that would perish in nature. It is quite likely that mutat ions occur almost as frequently in nat ure as under domesti­cation, but the unf avorable new forms are apt t o suffer early elimination. T here remains, ho,v­ever, a host of characters that are not detrimental to the individual, and such are not necessarily eliminated. T hey are teratological only in the sense that they are novel to the species, but they are of the same order as many of the specific dif­ferentire of feral species. T ake, for instance, the passerine birds-what a1·e some of their striking qualitative characters? W e find crossed bill

l\i1UTATION 173

(Loxia), crest ( cardinal bird and jay), greatly elongated tail (widah bird), bare throat (bell bird), wattle ( huia bird of New Zealand) , barb­less feather shaft ( paradise birds), barbs with­out barbules ( emu-\vren), twisted feathers ( Chi­rocylla). The plumage may be glossy black, snowy ,vhite, or of broken colors. Since such characters have arisen suddenly, by mutation, in poultry it is fair to conclude that they have probably done so in other birds. Of course there are many characters found in wild birds that are not found in poultry, but where we have evidence that many characters have arisen suddenly, dis­continuously, it seems probable that many others, of the same general sort, \vhose origin can not possibly be kno\vn have arisen in the same way. The experimental demonstration of the mutative origin of many characters makes probable such an origin for characters beyond the pale of ex­perimentation.

i71IUTATION vs. su:r.r:MATION OF FLUCTUATIONS

There are many who are quite willing to admit that mutations do occur, but hold that the part they play n1ust always be regarded as relatively less important than the summation of fluctua­tions. From this vie·w· the mutationist can ap­peal to the results of experiment. Does the breeder actually introduce ne\v characters into the organic ,vorld by summating fluctuations? D e Vries insists that the improvement that fol-

174 MUTATION

lows selection nearly or ,vholly ceases after four or five generations, and if selection be abandoned the race rapidly returns to its pri1nitive condi­tion. Such has been the experience of breeders of maize, sugar beets, and other crops, and of poultry1nen ·who have sought to increase the egg yield of f o,vl. P ermanent improvement, wher­ever made, has been effected either by hybridiza­tion ,vith a \-vild form possessing the desired char­acter or by preserving a fortunate sport-· a " Shakespeare," as Professor Hansen puts it. Such a sport is a new center from ·which further progress may start. Recognizing the futility of selecting merely those individuals having the old characters best developed, the most advanced breeders ( as at Svalof in Sweden), have system­atized the search for single mutations in the midst of extensive seed plats. 'l'his law of in1-proven1ent holds for animals like,vise. Four years ago I started several series of experiments to create, in poultry, new breeds by quantitative selection. In one of these I sought to re-create a uniform buff bird like the buffs that arose in China t,vo thousand years ago and are the par­ents of all kno,vn uniformly red or buff breeds. A bird with a red-a.nd-black plumage coloration of the Jungle fowl ,vas crossed ·with a "\iVhite L eghorn. The hybrids were white ,vith red on the wings and breast. I then planned to breed together the reddest of these birds and the red­dest of their descendants until I should have

lUUTATION 175

gained uniformly red birds. The second genera­tion of the hybrids did sho,v more red than the first, but during the last t,vo years no advance has been made. Again, a cock having a high single comb was crossed ,vith a hen having a typ­ical lo,v pea comb; the hybrid offspring had high combs '1-vith papillre placed high up on each side. An effort to establish by quantitative selection a high pea comb has failed. Dr. Castle tells me that his continued attempts to modify col or types of rats by quantitative selection have of late been inefficacious, since regression is very strong to­ward the original types. The evolution of the American trotter is often cited as a clear c.ase of the results of quantitative select ion. Yet is it n ot true that the advances in recent years have been quite as much determined by the evolution of the sulky and certain technical improvements in handling the trotter and t raining him? T he running record, the result of a larger selection, has, I understand, stood quite still for the last t,venty years. T hus even r:ace horses form no exception to the rule that selection, within given characters, soon reaches a period, and improve­ment must ·wait on the appearance of a ne,v char­acter by mutation.

T his conclusion, far f ron1 being opposed to D arwin, would doubtless have been cordially ac­cepted by him, as certain passages in his ,vritings indicate.' After describing the early unprove­rnent of the gooseberry, he says:-

1 Compare the instance given at p. 4S.

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" The ' London ' gooseberry ( whlch, in 1852, had al­together gained 333 prizes) has, up to the present year of 1875, nev·er reached a greater weight than that at­tained in 1852. Perhaps the fruit of the gooseberry has now reached the greatest possible weight, unless, in the course of time, some new• and distinct variety shall arise."

De Vries could not have put it better.

MUTATION AND NATURAL SELECTION

But, it is objected, the origin of characters by mutation can not account for adaptation as well as quantitative selection; and adaptation is the preeminent fact in natuJ·e, There is no good reason for drawing such a contrast. For the theory of mutation is nowhere incompatible with that of Natural Selection; there may just as well be, there just as truly is, a selection among dis­continuous variations as among quantitative va­riations. In the modern classification of varia­tions select.ion has come to be associated ,vith quantitative variations; but Darwin did not al­ways so associate it, as I have tried to sho,v. Any variation, of any kind or degree, must stand the test of fitness to survive. I f it can not meet the test it must be eliminated. In a field I had 300 young fowl, of ,vhich t,venty per cent were of mixed colo1·s, and eighty per cent were either white or black. Twenty-four of these birds were killed by crows, and all the dead were either white or black excepting one spotted white and buff. The solid colors aTe mutants; being con-

MUTATION 177

spicuous on the grass they were relatively unfit to survive, and so they ,vere eliminated. Again the elevation of the tail feathers by the hen is essential to successful coupling with the male; but this is impossible in rumpless hens, and they must all be infertile except for an operation. The wingless cock could successfully couple only ,vith bantam hens, as ,vithout mngs he could not balance himself while treading larger hens. These examples suffice to show how unadaptive mutations tend quickly to be eliminated. On the other hand, the split spur, the extra toe, the varied forms of comb, the frizzled and silky forms of plumage, even t he absence of the oil­gland seem, under the conditions of the poultry yard, to offer no important impediment t o sur­vival and propagation. We may conclude, con­sequently, that selection will act on mutations as ,vell as on graduated variations, eliminating the unfit and letting survive favorable 1nutations or such as are merely neutral. But, granted that the unfit mutations are eliminated, can such a case of close adaptation as is exhibited by the leaf butterflies ( l{allima and the rest) result from a series of mutations? D oes not the very per­fection of the adaptation indicate that the final touches have been of the quantitative order? Not at all. The perfection of the result may be due to a combination of adaptive unit characters. Bateson, who examined thirty-eight individuals from one locality, finds that they fall into four

178 i1UTATION

discontinuous groups with respect to the colora­tion of the under side of the \vings, a, "leaf­veinings " absent or nea1·ly so, ground nearly plain; b, ground \Vithout veins but with promi­nent black speckled spots; c, veins strong, no blotches; d, with blotches, ·with or without veins. Here at least three unit characters appear; dark lines (veins), black speckled spots, and blotches; but one or all may be absent from a given wing. Between presence and absence of the character no intergrades occur except possibly in the case of " nearly absent " veins. There is reason for concluding that even in ICallima new characters arise fully formed, and that these are numerous enough to affect all the detail of the pattern. If the combination of pattern characters is pro­tective, no doubt it ,vill preserve many individ­uals from elimination.

There is, moreover, still another way in which mutations may become adaptive; and that is by their possessor selecting a habitat that fits its organization. At the risk of encroaching on the subject of adaptation, assigned to another, I may give an illustration. The whole surf ace of the earth is scattered over with spores and seeds of plants and the resistant eggs and gemmules of various lower animals. Only if conditions are propitious ,vill they hatch or germinate. Some years ago a dam broke at Cold Spring Harbor in February and drained a lake of eighty years' standing. In the Spring a luxurious terrestial

l\1UTATION 179

vegetation sprang up on the lake bottom from seeds lying dorn1ant there. One Winter a ditch ,vas dug through a salt marsh, where the only higher plant ,>vas a species of marsh grass­S partina. The black peat cut from the ditch ,vas piled in a ridge by its side so high that it ,vas 110 longer coYered by the tide. In the Spring various roadside ,veeds spr.ang up along the ridges, forn1ing striking lines of vegetation run­ning athwart the marsh. In these cases the gern1s ,vere present, but failed to germinate until conditions suitable to their organization inter­vened. So, in genel'al, thel'e are abundant means of dissemination, and for almost every chai-acter there is a situation for which it is best suited. In that situation the new character will prove itself adapted to its environment.

THE l\IUTATION THEORY A KEY TO DIFFICULTIES

The notion of mutation, 1-vhen fully grasped, solves two difficulties ,vhich formerly confronted evolutionists. The first difficulty is the swamp­ing effect of intercrossing. If the usual result of crossing a new character ,vith its absence ,vere a blend of the two conditions, then the difficulty ,vould be a real one. But even in 1-vild species any unit character typically fails to blend when crossed with its absence. The unit characters of violets, shepherd's purse, and spots of beetles are experimentally tested instances. The characters

180 MUTATION

of domesticated organisms behave in the same way, as illustrated by poultry. Unit characters, then, in so far as they refuse to blend, ,vill not be swamped by intercrossing, but will reappear intact in a predictable proportion in successive generations.

The second difficulty which the mutation doc­trine solves is discontinuity between species. Species differ in the presence or absence of cer­tain unit characters. These unit characters are typically discontinuous in their origin. I-Ience it is futile to look for intergrades; as ,vell might one look for intergrades between carbon monox­ide and carbon dioxide. Species are discontin­uous because specific characters are discontin­uous; and s_peci:fic characters, in so far as they are unit characters, are discontinuous because the molecular changes upon which they depend are discontinuous.

It is rash at the threshold of any ne,v science to accept any one hypothesis to the exclusion of others. The president of our Association has taught us our duty to,vard multiple hypotheses. As in the ne,ver chemistry transitions between molecules a.re becoming a recognized possibility, so it can not be denied that some unit characters may a.rise gradually; or, as a. result of repeated crossing, show true blending and intergrading conditions. Many characters are indeed less or more because they have an ontogeny, and the adults stop at different points in the ontogeny,

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as seems to be the case with human hair color. In many instances of geographic variation a gra­dation of climatic conditions causes a gradation in the development of a unit character :all the way from invisibility to strong expression. Doubtless many important discoveries are about to be made in the field of graduated characters. :But from henceforth we must, I think, start in our studies of unit characters from the stand­point of their normal discontinuity. While we remember the services of De Vries in insisting on the normal discontinuity of unit characters, we shall, in considering the idea of the unit char­acter, recognize more clearly how great is the debt of biological science to the insight of Charles Darwin.

ADAP TATION BY

CARL H. EIGENl\llANN

I. DEFINITIONS

THE chief object in the life of any animal is to leave another like it in its place when it dies. To this end we find numerous adjustments and compromises, adaptations in animals or plants, to place them in harmony ,vith the elements of their physical or biological environment, or to coordinate the different parts of the same animal or plant.

v\Te have major adaptations, such as those of birds, mammals, etc., foi- aerial respiration, and those of fishes for aquatic. ,;v e have also minor adaptations for a particular combination of tem­perature, light, heat, and the other elements of the physical enviromnent. And, finally, we have adaptations fitting the animal to cope 1vith other animals for a mate and a home, to secure food and to avoid being food.

Aside from adaptations an organism consists of vestiges, and frequently of other characters, that are not adaptations.

Vestiges, "'e kno,v, a1·e the remnants of past adaptations. Specific characters "'hich are not

182

ADAPTATION 183

vestiges and are not no\v adaptations may also be past adaptations, or possibly they may be­come such in the future; it is only certain that they no,v do not particularly fit the species for survival. Some characters, ,vhile undoubtedly :adaptive, give the impression that they are over­done. The antlers of the deer, the fang of the saber-tooth, the po,ver of continuous gro,vth of the incisors of rodents, are all adaptations that !have in some instances proved to be too much of a good thing.

II. QUESTIONS

In the ,vords of "\V eismann, the most ardent of the Darwinians, " Adaptations arise ·whenever needed if they are at all possible."

Adaptations have usually .been looked upon .as adjustments in the organism to its environ­ment. The suggestion has more recently been made that adapted environments and habits are ,Selected by animals adjusted to them.

Is a man healthy and strong because he prac­tises athletics, or is he practising athletics because his strength inclines hirn to athletic sports? We have all been modified by our environment and by our activities. It is at least suggestive that some of us haYe never taken to pole-vaulting and should not have n1ade a record if ,ve had. Evi­dently there is a d:iff erence bet,veen the questions of the origin of adaptations in the individual and the origin of a111 adapted fauna.

184 ADAPTAT ION

The latter is a comparatively simple question. No one, for a moment, would claim that the entire fauna of any particular area of land, or river, or ocean arose ,vhere it resides,-beca1ne adapted in its present habitat. Adapted faunas are only in small part autochthonous; in large part they a1·e made up by selective migration.

III. ORIGIN OF ADAPTED FAUNAS

For a consideration of the origin of adapted faunas I would invite attention to the fresh ,vater, and cave fish-faunas.

The major conditions distinguishing fresh waters from the ocean as an environment for fishes are these: (I) The fresh water contains a very much smaller per cent of salts in solution than sea ,vater. (2) It is, with few exceptions, in continuous locomotion in one direction. (3) I t contains sediment. i :finor characters distin­guishing fresh ,vater differ in different localities.

F resh-water fishes are not a group different from salt-water fishes. i f any salt-,vater fishes can enter fresh water, and ,ve may for present purposes assume that all candidates for fresh­,vater existence are adapted or readily adaptable to the fresh ,vater. Adaptations to the second and third of the fresh-water conditions imply pe­culiarities in habit or structure not possessed by all fishes, and these must, in the main, have been acquired by the marine fishes before they could enter and maintain themselves in fresh water.

ADAPTATION 185

The downward current and sediment, if the lat­ter is not too abundant, are not obstacles suf­ficient to keep an adult fish from entering fresh ,vaters. The eggs and young furnish the point of attack. Among oceanic fishes we have many that have pelagic eggs, others that have adhesive eggs, others that have heavy cohesive eggs, others that have filaments for the attachment of eggs, while others harbor their eggs.

Currents would naturally tend to carry pelagic eggs into the ocean, and as far as I know only one fish ·with pelagic eggs has succeeded in estab­lishing itself in fresh water, and it, the eel, to the present day, descends to the sea to deposit its eggs!

The other types of eggs of marine fishes are all found in fresh waters, and it is certain that in many cases the possession of eggs of one or another of these sorts has enabled the fish to establish itself in fresh wate1·. Thus the major adaptations ,vere acquired by the ancestors of fresh-water fishes before they ·were eligible to a fresh-water existence. Innumerable minor adap­tations to the peculiar combinations of heat, sed­iment, light, etc., found in each selected locality, have no doubt arisen in such localities.

,vhen a new "vater area arises, selective migra­tion is the method of origin of the adapted fauna. The vast territory containing our North Amer­ican lakes and streams north of the southern line of glaciation, the area from the Arctic south to

186 ADAPTATION

near the Ohio River, was covered a fe,v thousand years ago with a sheet of ice. It contained no environment suitable for :fishes. The entire fauna and flora of this area, including the fish­f auna, are composed of immigrants that moved in as the ice moved out, and selected the places adapted to each species. While a few of them have become modified since their advent into this area, their fundamental and even their minor adaptations ,vere acquired else,vhere than in their present home. Their adaptation is due to the selection of an adapted environment.' The entire area is unsuitable as a p[ace for the study of the origin of a[l but a few miinor adaptations.

T he check by cold has not been placed on any individual migration or set limits to the adult. Rhinichthys dulcis living in glacial ,vaters and warm springs and the n1any species adapted to the great r ange of variation in the temperature in any of our temperate lakes sho,v this. The temperatu1·e factor determining distribution is set rather by the adaptation of the eggs to ,varm or cold water. Our trout, salmon, and white fishes breed largely in ,vinter ,vhen the tempera­ture is low. The rate of development of their eggs, like that of all cold-water eggs, is slow.

• Of the 15~ species of fishes of the Great Lake basin, only 26 species and varieties, 17 per cent of the total, are peculiar to the area. Five of these are but varieties of more southern species, and the other in more than represent the extent to which the fauna has become adapted in this area, for eight salmonids and eight cottids a·re cold water species that may have 'been crowded out of the region to the south of the basin, by the encroaching heat after the passing of the last glacial epoch,

ADAPTA.TION 187

The ,varm-,vater species are ,varm-,vater species not because their individuals are incapable of entering cold ,vater, for they do, but because their eggs ,vill not develop in anything but water n1ucb ,varmer than that in ,vhich the eggs of cold­" -ater species develop. Their eggs are quickly developed, they aJ·e adjusted to fluctuations in temperature, and they respond to such fluctua­tions in temperature by hastening or slomng their rate of develop1nent.

The origin and modification of the cave fauna giive a concrete example of the change of loca­tion resulting from predestined major adapta­tions and subsequent minor adjustments. Caves, at the present time, are being colonized by immi­gration of salamanders of the genus Spelerpes and other animals that have become adapted to a cave existence ·while living in the dark under rocks, bark, and in other similar places. The adaptation to the conditions of cave existence in this case determines the change of location when­ever a cave presents itself.

That minor adaptations occur in these after they have become exclusively cave forms is shown by the structure of the permanent cave salaman­ders of l\iissouri and Texas. These have, in large measure, lost their color, and have degen­e1·ate eyes.

Not infrequently ,vhere ,ve have extreme adap­tations to a particular and a peculiar environ­ment, such as al'e found in the blind fishes to the

188 ADAPTATION

caves, or the ability of ichneumon flies to detect and lay their eggs in deeply hidden grubs, we do not really need to account for the extreme adap­tation to the extreme environment. The envi­ronment and the adaptation may have developed together, as armor-piercing projectiles and armor have so developed together. An illustration is found in the origin of the cave fishes of I(en­tucky, and still more of those of Cuba.

The cave fauna of l(entucky, so highly adapted it would be hopelessly lost if removed from its peculiar environment, is the result of selective emigration, immigration, and local adaptation. I t has become adjusted ,vith the development of the environment it inhabits. At H orse Cave, l(y., a mde valley extends north and south. T ributary valleys come f ro1n the east and '\>vest. T he hills bordering these valleys are limestone capped with sandstone. The north-and-south valley "\-Vas formed by the H orse Cave R iver, ·which originally flowed over sand­stone like that capping the bordering hills. No doubt it had a fauna as varied as that of any surface stream. T he stream first cut through the sandstone, then into the limestone, in ·which it gradually dissolved an underground channel. To-day not a sign can be seen on the surface of the streams that are responsible for the valleys about Horse Cave. At least one of them rushes through lofty chambers one hundred and eighty­five feet beneath the streets of H orse Cave.

ADAPTATION 189

With this change in the environment, ·with the disappearance of Horse Cave River from the surface, its inhabitants \Vere con1pelled to mi­gTate. They moved in t\vo directions to adapted environments. 'rhe shore-fishes, channel-fishes, etc., depending on light to find their food and mates, moved out to the Green River, ,vhere their descendants live to the present day. 'fhe fishes negatively heliotropic, nocturnal, or stereotropic, moved into the holes dissolved in the bottom of the river, f ollo,ved its subterranean development, and their descendants live to-day in the stream \vhich no,v flows entirely below the valley. They are colorless and all but eyeless, and have, no doubt, acquired this exaggerated adaptation to their present abode since their immigration. T he major adaptation to the cave existence, the po\ver of finding their food and mates ·without the use of light, they possessed before the fonnation of the caves, and it is responsible for their present habitat.

Primarily blind fishes do not have degenerate eyes because they live in caves, but they live in caves because their ancestors ,vere adjusted to do ~•ithout the use of eyes. The degeneration and disappearance of their eyes form another matter.

VVherever in the past environ1nents arose lack­ing light, they became, and still are, the gather­ing place of those not dependent upon light.

The Cuban blind fishes offer another example of the concomitant development of a peculiar

190 ADAPTA'l'ION

and complex environment and its peculiar fauna. The blind fishes of Cuba are members of a family of marine fishes, but live in fresh ,vater in caves of central and western Cuba. They have undoubtedly arisen with the environ1nent in ,vhich they now live. The caves are enlatgements of rifts in coral reefs. They can be traced from the hills near l\1atanzas to the shore of Cuba. One of the cracks is seen in the naked coral beach near the Carboneria at the 1nouth of l\1atanzas B ay. Another can be traced a little ,vay inland, but a few feet above sea level. The former must contain salt ·water- the latter certainly contains fresh ,vater. I n places similar to the former the nearest marine relatives of the cave blind fishes are found, with eyes. In the latter cave blind fishes are abundant. Evidently the ances­tors of the cave blind fishes have ahvays lived in the crevices in which they now live. "\iVhen these crevices were below the ocean's surface they con­tained salt ,vater. As the land arose the salt ,vater ,:vas gradually replaced by fresh ,vater, to ,vhich the fishes as gradually became adapted. The fishes have literally gro,vn up ,vith the country.

Selective migration, the migration to adapted locations, is the chief factor contributing to the origin of adapted faunas. This factor "cha:nge of location" is to the origin of adapted faunas ,vhat the " change of function " is to the origin of adaptive structures.

ADAPTATION 191

IV. ORIGIN OF ADAPTATIONS

A . T HE P RonLE:i\L The question of the ori­gin of the adaptations themselves is much more difficult. I f co1nparatively fe,v or no ne\v adap­tations have arisen in any one neighbol'hood, nevertheless all these modifications must have arisen some\vhere and should be accounted for. l\1any explanations have been offered. The sup­porters of some of the explanations adhere to them \vith the fanaticism of religious belief. But it is necessary to have been reared in the faith to see all that is claimed for them.

Hereditary succession may follo\v a horizontal line or one that swerves up or down. I n other ,vords, successive generations may be alike, in which case the species remain in statu qiio, or subsequent generations may deviate from their parents in one or more points.

All deviations from the horizontal must start in the germ, or roust become located in the germ. T he question of the origin of adaptive deviations is the question of ho\v and why adaptive ger­minal modifications arise, or how adaptive so­matic modifications are transferred to the germ. I n either case it is the question of how the straight line of exact hereditary repetition may be caused to s,verve in a definite dir,ection to reach an adaptive point. T his is the question of the pres­ent generation, perhaps of the entire twentieth century. '

192 ADAPTATION

To be effective the deviation must be pre­served, but it is not necessary to ent~r into any discussion of Natural Selection. This very occa­sion bears evidence of the all but universal ac­ceptance of the principle. It forms part of nearly every theory of the origin of adaptation.

B. THE !\1:ATERIAL. In discussing the origin of adaptations I shall confine myself mostly to the brief examination of some of the adaptations in the American Characins, to determine, if pos­sible, to what extent different factors of evolu­tion have contributed to their origin.

The Characins are fresh-water fishes no,v in their prime in tropical Africa and in tropical America.

I hope I need not apologize for confining my­self to a bit of the wealth of that continent, South America, which has been the training ground of Darwin, Wallace, Bates, Mi.iller, and so many of their supporters.

In America there are known about six hun­dred species ranging from the borders of the United States to Patagonia. Different mem­bers are adapted to nearly all possible fish envi­ronments, both physical and biological. There are mud-eaters without teeth, flesh-eaters with teeth like a mowing-machine, and others with long fang-like canines projecting through the upper jaw when the mouth is closed. In the Es­sequibo River I caught over forty species in one day. Some of these minute translucent species

PLA'rE III.

A. F 1,w 01' T HE: NU)IIWOUS T ,r£s 0 1> T EETH IN THE CaARACINS.

(From l>hotogrnph:s by the nnthor.)

J. Un1>hiodon \'ulpinus Spi s-. 2. AttLynrlflS l)i mnculntus bN\'OOl'tii Gill. a. Scrra~u,hno lrnmcralia Cuv. & Vol. 4, Hcnoch,lus whe11thrndi Gnrnrnn. 5. Aces1.rorh ync;hus folCJatus B loch. 6. Uoplerythrinutt unit::eniotuti s,,1~. (Head retiemlJles 1bat of Amia.) 7. Lcporinus conirot1t1•is Steindachn er. 8. Procbilotlus scrorn Stcinclnchncr. ~- A1>bi'>ChUTt1.s. demat.ua Eigenmnun & Kennedy.

2

P'.,.\TE l\'.

SO~IE S1~1ILARITIES IN TUE Cll,IRACINS.

(All figures after Steindachner.)

1. Luciocharax insculptus. a G~rpike.like C:hnrncin. 2. Salminug amni$, a Salmon -l ike Charncin . 3. Prochilodno h:>n~irostri~. n Sncker-lil,e Clrnracin, 4. Chalcinus ma~dalenre, a rretth water ll crring-liko Characin, 5. G:1i-1t-ropclecus mnculotn~. ft flying Charncin. G. )il yltul! kn<>rii~ n Pompnno.like Characin. 7. ~imnosvunud unifii,cinms, n Cyprioo<lout-like Characin.

--- 5

ft

ADAPTATION 198

butTO\V in the sand in the bottom of the l'iver, others fly ,vith ,ving strokes thxough the air above the river, and others occupy all possible spaces bet,veen. I n appearance they parallel our gar­fish, our pickerel, our top minno"vs, our pom­pano, our trout, our minno,vs, our suckers, our darters, our fresh-,vater herrings and shad; and besides these there are a variety of shapes and sizes and adaptations not to be found in other fishes. Chief of these is the series ending in a true flying fish, i.e. a fish with wing-like pecto­rals, large muscles to move them, and the ability to propel itself ,vith ,ving strokes along the sur­f ace of the ,vater for forty or more feet, and to continue its flight for five or more feet in the air.

C. CAUSES OF ADAPTATIONS. The causes lead­ing to new adaptations may be intrinsic OT ex­trinsic. The theories of N ageli, W eismann, and, in part, of D arwin and D e Vries, are based on intrinsic causes; those of Buff on, Lamarck, Gu­lick on extrinsic.

D. ORTHOGENEsrs. Nageli, and in a modified form Eimer, W aagen, Osbo1·n, ,vhitman, and others, have sho,vn that lines of evolution are orthogenic, predetermined in definite directions. According to Nageli direction is maintained by the make-up of the protoplasm of the individual. According to V\T eismann direction is given by the process of germinal selection, helped out by per­sonal selection. By Osborn and others it is recog­nized but not explained.

194 ADAPTATION

The Characins offer us the very best imagi­nable proof, both for orthogenesis and against its universality. The fact that lines of evolution radiate in so many directions in this family is ab­solutely conclusive proof that there are many possibilities, that evolution to adaptive points may not only take place along one line or par­allel lines, but along very many diverging lines. On the other hand, the fact that there are lines with but few breaks leading from the general­ized central type to such aberrant forms as the minute sand-burro·wing Characins, duplicating our sand darters, or to the death-dealing Serra­salmo, or tbe flying Gasteropelecus, sho"vs that, a path of adaptive modification once entered upon by these fishes, evolution along that line may take place, even beyond the point of highest ad­vantage. These lines are not parallel and can not therefore have been the result of the inherent make-up of the family. 1 They have in some \vay been determined and are being follow·ed to the limit.

E. MUTATIONS. The possibility of divergence in many directions has been expe1·imentally demonstrated by De Vries, who, ·with others, has claimed that the line of adaptive modification is broken, not bent. VVaiving the question of whether the difference bet,veen the bend and break is one of kind or degree, permit me again

• Similar cha racters like a pair of canines or ctenoid scales have appeared in very diverse genera both in Africa and in South America.

ADAPTATION 195

to point out instances of both in the Characins. I do this fully acware of the fact that some of our experimentalists have claimed that evidence in favor of mutation ,vould not be noted by the sys­tematic zoologist. It is, ho,vever, quite certain that evidence for mutation can not be obtained by experiment only. I have several times found evidence in f avor of it in the Characins.

In the Tetragonopterinre there are parallel genera or subgenera, as we care to look at them. One series has a complete lateral line; the other series has pores developed on but a f e-..v scales. No doubt one has been derived from the other­not once but several times. One species, I-I e1ni­grar1wnus inconstans, is evidently mutating. T,vo of the four specimens known have a com­plete lateral line, in the others it is quite short.

Among hundreds of specimens of another spe­ci,es with an incomplete lateral line a single mu­tation has been found v,rith a complete line. lJloenkhausia australe by mutation is producing, or has produced H ernigramnius. I n such cases we have, if a bull is permitted, individuals that are specifically alike but generically different.

While ,ve have many undoubted cases of muta­tion, there are many reasons why we should not jump to the conclusion that all adaptations have so arisen.

One example of continuous variation leading to an adaptive point is found in some localities of Nicaragua. H ere the species of Astyanax

196 ADAPTATION

reneus, elsewhere with t"wo maxillary teeth, is varying in the old-fashioned way towards a form whose entire maxillary is covered with teeth, i.e. it is varying to become a H emibrycon. Of thirty-five specimens there are nine with t,vo teeth, two with three teeth, five with four teeth, five with five teeth, five ,vith six teeth, five with seven teeth, three with eight teeth, and one with nine teeth in the maxillary. No doubt there are some who will claim that these are really muta­tions, not variations, and I am perfectly willing that they should put this balm upon their preju­dices.

The nature of the progressive degeneration of the eyes of blind fishes argues also against the uni­versality of the origin of adaptations by muta­tion. The degeneration of the eyes of such fishes is a continuous process. The eyes of individuals during their lifetime undergo a continuous de­generative modification leading sometimes to the entire elimination of the eye in the old. The retrogressive changes begin in ever earlier stages of the ontogeny. The differences bet,veen indi­viduals a.re so slight as to exclude the possibility of personal selection, ,vithout which either muta­tion or Natural Selection is incapable of produc­ing results.

There is no evidence that mutation has had any more to do with the production of degener­ate eyes than special creation, and ,ve can not even imagine how the degenerate eyes n1ight have

ADAPTATION 197

rurisen by n1utation. Their degeneration is due to orthogenesis or to use-transmission.

F . ENVIRONl\IENTAL ADAPTATION lVIAY BE I NTRINSIC OR EXTRINSIC. 1 . Geographical va­riation or divergence. T he facts of geographical distribution 1nake it certain that adaptations have not arisen through intrinsic causes only.' I n fact, they n1ake us doubt at times whether intrinsic causes have had anything ·whatever to do ,vith the origin of adaptations. I f all forms were the result of mutation, due to intrinsic causes, there is no reason ,vhy a large river such as the Rio San Francisco should not contain all the modifications possible to the genera inhabit­ing it, for Shull has sho,vn that ne,v forms may arise in a restricted area. But it does not. Of equal sized streams belonging to different sized r iver systems the one belonging to the larger sys­tem harbors a larger number of species of any genus. 2 And other things equal, the wider the distribution of any genus the 1nore species corn-

' Tower: Evol·1ttion in Ohrysomelid Beetles, p. 314, says: " ... All evidence showing them (mutants) to be most rigorously extermi­nated by natural selection. On the other hand, the study of geo­graphical distribution and ,•ariation gives the strongest of drcumstantial evidences for dh·ect and rapid transformation in i-esponse to environmental stimuli as to the result of dispersion . . . according to the method of trial and error, ,vith natural selection acting as the conservator of the rnce l>y limiting the variation to a narrow range of possibilities."

• Bean Blossom Creek of Monroe County, Indiana, draining an area of about 250 square mi les, is known to harbor in two miles of its course 44 species of fishes. The Colorado, draining an area nearly 1,000 times as large, contains but 33 species of fishes. But Bean Blossom is part of the Mississippi basin that far exceeds the Colorado basin in size and harbors at least 200 species. The still larger Amazon basin harbors at least 700 species.

198 ADAPTATION

pose it. In nearly all cases where a species is distributed over a ·wide, discontinuous unit of environment, i.e. an area broken up into isolated parts, the parts contain forms that are meas­urably different from each other.

A most instructive example is furnished by the Chara.cins. Astyanaa:: f asciatus is found from Patagonia to l\l[exico, except at Panama and the Rio Parahyba. It differs in different localities, and in the Rio Parahyba, near Rio de Janeiro, and at Pana1na the differences have be­come of specific value. T he species is continued in southern Mexico as Astyanaa:: ceneus, and in northern Mexico as Astyanaa:: argentatus. I n other words, in those cases where the divergence has gone far enough we call the divergents spe­cies, in those cases ,vhere they a.re diverging, vari­eties. These geographical varieties are species in the making, just as t1·uly as the elementary species of De V ries.1

Isolation is not ahvays accompanied by differ­entiation. S01ne species of Galaxias in Patago­nia and .1-\.ustralia are identical, ·while those in different parts of Patagonia are different. Geo­graphical isolation must lead to differentiation if the isolation forces the individuals to live in places on the ,vhole different f ro1n their original home. A species (.1lstyanaa:: fasciat1~s) may be all but identical even if isolated in diffe1·ent rivers

• The different diverging li11es will be fully cons.idered in my monograph on the Characins, now in preparation.

ADAPTATION 199

from Niexico to Patagonia, provided it may oc­cupy the same sort of envirorunent in each stream. There is more environmental differ­ence in the different parts of a cross-section of a river in the Amazon region, or in a mile of the length of a small brook, than there is in the pelagic region of streams from 1\1exico to Pata­gorua.

2. Geographical convergence. Each river is nliade up of many different units of environvient. The pelagic area is but one of these. 1\{uddy bottom, ,veedy bottom, stagnant water, swiftly flowing water, are other units. Each has its peculiarly adapted fauna. Different members of the sa1ne family may belong to different eco­logical series, and different ecological groups are n1ade up of members of different families. I n shallo,v, swift water over gravel, in a small stream, the adaptations required are a heavy body, strong pectorals and ventrals, on which the fish sits and whiich are held in readiness for sud­den springs. The conditions and adaptrutions are the same whether the stream be in North America, in Cuba, or in South America. Fishes are adapted to the conditions in each locality, but the adapted faunas in the three areas are not re­lated. I n North America, darters, or diminu­tive perches, are adapted to this niche; in Cuba it is members of the marine Gobies, and in South America members of the versatile Characins and catfishes. Shape and many other things count

ioo ADAPTATION

for little among fishes. All shapes occur at nearly all times and nearly all places.

Similarly, blind fishes adapted to caves or other dark places have arisen in many places, but are not necessarily related to each other. The blind fishes of Point Loma are Gobies, and have their nearest relatives in neighboring waters. Those of the Mississippi valley belong to the Amblyopsidre, some of \;vhich live in the terranean streams of that valley. The caves of Cuba de­rived their blind fishes from the cracks of the coral reefs in which caves ,vere farmed. In South America their nearest relatives are the nocturnal catfishes of Brazil and the blind fishes of Pennsylvania have their nearest Telatives in the nocturnal catfishes of Pennsylvania.

The burrow·ing lizards of Florida living as earthworms do, look so much like earth,vorms that the very chickens do not discriminate against them.

3. Geological convergence or parallelisrn. Geo­logical records of the simultaneous and similar changes in the form in the mass of species of any area during changing physical conditions are not wanting. For instance, Scott says:-

"The steps of modernization, which may be observed in following out the histo•·y of many different groups of mammals, are seen to keep curiously parallel, as may be noticed, for example, in the series of skulls figured by l{owalevsky, where we find similar changes occurring in such families as the pigs, deer, antelopes, horses, ele-

ADAPTATION ~01

phants, etc. Indeed, one may speak with propriety of a Puerco, or Wasatch, or White River type of skull, which will be found exen1plified in widely separate orders."

One adaptation has not arisen once but many times.1 To repeat, " Adaptations arise ,vhen­ever needed, if they are at all possible."

4. Origin of geographical and geological di­vergence and convergence. All these facts tend to show that adaptations have arisen as the result of the peculiarity of the environment. How?

It has been demonstrated many times that the individual is modified by his physical environ­ment. It is claimed on the one hand that the deviation is maintained by its transmission to the germ-plasm, and thus the next generation; and, on the other, that the environment, in some cases at least, directly affects the germ-plasm.

There is a third possibility. I n some localities the individuals of certain species are very dark, in others they are practically without color. I f the latter individuals are examined closely it is found that they are abundantly supplied ,vith chromatophores, and only the needed environ­mental stimulus is lacking to bring out the strong color. This is not a matter of the simple expan­sion or contraction of the pigment, which may take place in a f e,v moments, but the develop-

2 Among characters that have appeared several times inde­pendently in the Characins may be mentioned: The incomplete lateral line, the scaled caudal, three series of teeth in the pre­maxillary, a pair of canines in the lower jaw, ctenoid scales, incisor-like teeth.

ADAPTATION

ment of an excess of color under the necessary conditions.

I t is possible that other nascent intrinsic adap­tations are present in different individuals, unno­ticed and inconspicuous until the requisite envi­ronment causes them to reach the limit of their individual power, that they are environmental adaptations only in appearance. On the other hand, it is certain that in cave animals there is a gradual bleaching with the removal from the light. I t is at first purely ontogenic. But no scheme of selection 1 will account for the pro­gressive reduction in the pigment in successive generations. Nevertheless the color becomes less in each generation. And in the final establish-1nent of the bleached condition in hereditary suc­cession even in the lighit we have an instance of the transmission of an environmental adaptation.

Where environmental adaptation is the result of a struggle ,vith the physical environment, the struggle is entirely independent of the rate of re­productioJ?.. The individual n1ust adapt himself to heat and cold ,\1hether alone or not. T e1nper­ature and other elements of the physical environ­ment affect many individuals at one and the san1e time. For this reason the physical envirorunent, ,vhen it makes its presence felt, operates in a dramatic way. It attacks the mass, so1netimes killing thousands of the non-adapted at one stroke. As long as it does not kill all, the kill-

' :Mutation is ruled out without selection.

ADAPTATION ~03

ing must be selective and preserve both those ontogenetically and those innately adapted. The attack being on the mass of species and individ­uals, it tends to preserve those that are alike.'

G. F U NCTIONAL ADAPTATIONS. The whales li,ing like sharks look like the1n. Osborn re­n1arks: " If a primate begins to inlitate the hab­its of an ungulate by becoming herbivorous, it also begins to acquire the dental cusps of an un­gulate in about the same order as these cusps " 'ould arise in an ungulate."

I could paraphrase Osborn's words for the Characins n1any times. The Characins have taken on the habits of many fishes and hav,e par­alleled them " 'hile they diverged from each other. A certain habit and habitat in fishes carries with it a certain regulative adaptation. Living as a sand-darter does, carries ,vith it a sand-darter shape. The question that confronts us first is not, ,vhy does the sand-darter habit carry ,vith it a certain form, but ,vhat caused Characins to adopt the darter habit?

\Vhat caused Osborn's primate to begin to inli­tate the habits of an ungulate? What caused different Characins to begin to eat mud, crusta­ceans, plants, plankton, and each other?

Overproduction of individuals leading to cro,vding, the struggle ,vith the biological envi­ronment for food ( or light in the case of pi.ants) ,

' No more striking: example is found than in the old but uniform deciduous habit of plants of the temperate region.

!!04 ADAP TATION

causes all accessible places to become inhabited. Food itself is dependent on other food, and this ultimately on light, heat, depth, natul'e of bot­t om, current, and other elements of the physical environment. The habitat once selected, the effect of the changed physical environn1ent ,vill cause the changes already discussed, and the changed biological environ1nent ·will cause an arii1nal to adopt a changed mode of existence.

I t is again possible either that innate charac­ters in cer tain individuals of a crowded com­munity cause the1n to migrate in cert ain direc­tions, or that chance individuals migrate, and that intrinsic or accidental extrinsic causes then start new activities. I t is certain that ne,v activities once adopted the result is individual modifica­tions.' I t has long been claimed and as vigor­ously denied that these adaptive individual devia­tions are tl'ansmitted.

T he factors of both Buffon and Lan1arck hinge on the possibility that so1natic modifica­tions are trans1nissible to the reproductive cells. We have not been able to imagine ho·w somatic changes could so influence the reproductive cells that they could, in their turn, produce individuals

• \Ve can imagine that this process of overproduction and con­sequent adoption of diffe1·ent II reas r~ay take place m a sm!lll basin, but certainly the larger the basin the g:rea~er the d1vers1ty of conditions, the greater chance of comparative isolation m d1 f ­ferent sor ts of em•ironments, and the greater the number of species. . . .

No small stream long isolated contams many species of a given genus. Notable exceptions are Orcstias in Lake 1'iticaca, and Chirostoma in the Lerma. \Vhat applies to the species of a genus applies with equal force to the genera of a family.

ADAPTATION fl05

possessing in a measure the same chai-acters. Nevertheless, the transnussion of individual en­vironn1ental adaptations has been established.

No cases of the transnussion of functional adaptations as unquestionable as those of envi­ronmental adaptations are on record.

It has seemed difficult indeed to devise experi­n1ents which ,vould prove that the small somatic changes possible during a lifetime are tr.ansnut­ted. We were not sanguine enough to suppose that in one generation modifications could be effected and transnutted that ,vould surpass nat­ural variability, and ,vhich could, therefore, be recognized as transmitted characters. I have long been convinced that the progressive degen­eration of the eyes of cave vertebrates, coupled ,vith the differential degeneration of different parts, is due and can be due to nothing but the transmission of functional adaptation. I can not altogether regret that this evidence does not seem to have convinced many others.

The possibility of the transnussion of somatic characters to the reproductive cells has been shown by the transplantation of ovaries in chicks by Guthrie. He found that a black hen con-

• taining an ovary transplanted from a ,vllite hen, mated with a white male, did not give ,vhite chicks exclusively, as the non-transnussibility of somatic characters would require, but that more than half of the chicks were spotted ,vith black. Also that a ,vhite hen containing an ovary trans-

206 ADAPTATION

planted from a black hen and mated ,vith a black n1ale gave young all of which were spotted. These results, if based on rigorously selected n1aterial, ought to convince all but a packed jury that somatic characters are transmissible to the reproductive cells. If any one kno",s of de­fects in Guthrie's material it is incu1nbent on hin1 to furnish or define material free from all objec­tions on ,vhich his experiments may be repeated; for the method promises a final ans"'er to this n1uch debated question.

H . CONCLUSIONS. "'\i\7e are forced to the in­evitable conclusions that adaptations are not chargeable to one factor, but that sometirnes there has been one, sometimes another, and more fre­quently several factors have cooperated to bring about the adaptations in any one animal.

It is but justice to Darwin to say that he did not pin his faith to the theory of Natural Selec­tion exclusively. Darvvi.nism is broader than neo-Dar,vinism, ,vhose insufficiency to account for all adaptations becomes daily more apparent.

After fifty years of study of the origin of adaptations a single sentence from Darwin's Origin of Species approaches closely to the gen­eral conclusions of to-day, and, "lest we forget," it should be emblazoned on the walls of every Biological Laboratory: " These la,vs, taken in the largest sense, (are) growth, ,vith reproduc­tion; inheritance, which is almost implied by re­production; variability, from the indirect and

ADAPTATION ~07

direct action of the external conditions of life, and from use and disuse; a rate of increase so high as to lead to a struggle for life, and as a consequence Natural Selection entailing diver­gence of characters and the extinction of less in1proved forms."

I. A P LEA }' OR THE NATURALIST. I can not close this paper ,vithout a plea for the naturalist and systematic zoologist. "Analysis," says Rus­kin, " is an a bonunable business. I am quite sure that people who ,vork out subjects thor­oughly are disagreeable wretches. One only feels as one should ,vhen one doesn't know much about the matter."

The systematic zoologist is liable to lose sight of the ,voods on account of the trees, and follow the example of Jean Paul Richter's Quintus F'ixlein, ,vho collected a vast number of typo­graphical errors, assured the public that valuable conclusions could be drawn from them, and left it to some one to draw them.

The imagination is in Biology as elsewhere the guiding spirit. The trouble is our imaginations are sometimes too heavily loaded with statistics and at other times they fly ,vithout the balancing kite's tail of facts. The Paleontologists have contributed so much to speculative zoology be­cause their imaginations have been kept alive by bridging their numerous gaps and because they have not been hampered by too great a ,vealth of material.

~08 ADAPTATION

Whether ,ve amputate eyes and legs to see them regenerate, determine the chromosomic dif­ferences between related species, centrifuge eggs, or invent new plants, potato beetles, guinea-pigs, or poultry, match butterflies, count scales, or measure fossils, we are all at work on the prob­lem of problems, "The origin of adaptations."

Experiment is the watchword of the day; but while ,ve are experimenting in our back yards we should not lose sight of the beauty and the impor­tance of t!he experiments in landscape gardening and zoological gardening, that are and have been going on in our front yards that extend from here to Cape Horn.

DARWIN AND PALEONTOLOGY BY

HENRY FAIRFIELD OSBORN

ON l\1arch 4, 1860, Charles D ar\vin wrote 1 to Joseph Leidy of Philadelphia:-

" Your note has pleased me more than you could readily believe; for I have during a long t.ime heard all good judges speak of your paleontological labours in terms of the highest respect. ~lost paleontologists ( with some few good exceptions) entirely despise my work, consequently approbation from you has gratified me much; all the older geologists with the one exception of Lyell, whom I look at as a host in himself, are even more vehement against the modification of species than are even the paleontologists. I have, however, been equally surprised and pleased at finding that several of the younger geologists, who are now doing such good work in our own. geological survey go with me and are as strong as I can be on the imperfections of geological record.

"Your sentence that you have some interesting facts ' in support of the doctrine of selection, which I shall

1 Dar"~n's letter to Dr. Leidy is under date of March 4, 1860, in reply, as he states, to Leidy's letter of December 10, 1859.

On March '27, 1860, upon the recommendation of Isaac C. Lea and Dr. Joseph Leidy, Darwin was elected a corresponding member of the Philadelphia Academy of Natural Sciences. It is probable that to the Philadelphia Academy belongs the honor of having been the first foreign society to accord this great work official recognition. This recognition was appreciated by Darwin, as is shown by his reference to it in a letter to Sir Charles Lyell, dated May 8, 1800.

The 01·iginal letter is in the collection of Dr. Joseph Leidy of Philadelphia, nephew of the great anatomist.

209

~10 DARVVIN AND PALEONTOLOGY

report at a. favourable opportunity,' has delighted me even more than the rest of your note. I feel convinced that, thougl1 as long as I have strength I shall go on working on this subject, the sole way of getting my views partially accepted will be by sound workers show­ing that they partially accept them. I say 'partially,' for I have never for a moment doubted that, though I can not see my errors, much in my book will be proved erroneous." ·

Fifty years ago paleontology ·was an embry­onic science so far as natural philosophy is con­cerned; beyond the grand outlines of change in the ,vorld of extinct mammals and reptiles Dar­win knew little of its processes or results. In the letter cited above he is encouraged by Leidy's promise of paleontological support for the gen­eral doctrine of evolution; he is even more grat­ified ,vith the passage relating to Selection. In other ~,ords, in this char.acteristically candid let­ter Darwin appeals for evidence f ron1 paleontol­ogy in support of evolution; he hopes that sound ,vorkers ·will partially accept his views regarding Selection; he does not for a moment doubt that much of his vie,vs regarding Selection will prove to be erroneous.

A year later, April 26, 1861, Dar,vin writes to L. Davidson, the great authority on brachiopods, asking him to undertake a piece of ·work ~1hich would test the doctrine of evolution.

" . . . in that book [the Origin] I have made the remark, which I apprehend will be universally admitted, that as ci whole, the fauna olf any formation is interme-

DARVVIN AND PALEONT0L0GY 211

diatc in character between that of the formations above and below. But several really good judges have re­marked to me how desirable it would be that this should be exemplified and worked out in some detail and with some single group of beings. Now every one will admit that no one in the world could do this better than you with B rachiopods. 'l'he result might turn out very unfavoul'able to the vie1vs which I hold; if so, so much the better for those who are opposed to me. . . . I know it is highly probable that you may not have leisure, or not care for, or dislike the subject, but I trust to your kindness to forgive me for making this suggestion." 1

I shall sho,v that the sanguine as " 'ell as tite questioning prophecies 0£ these epistles 0£ 18130 and of 1861 have been fulfilled to the very letter by paleontology; but in order to place the ,vhole matter in its true perspective, and brighten rather than dim the grandeur of D arwin's fame, let me first b1·iefl.y picture paleontology as it ,vas in 1859 and as Darwin himself knew it even up to the time of his death in 1882.

I t is true that n1odern, or D ar,vinian, paleon­tology, as distinguished from the older, or Cuvie­rian paleontology, dates from a decade after the p ublication of the Origin, or from 1868, when ,v aagen 1 first exactly and minutely described the mutations which occur in a descent or phy­letic series of ammonites, and it is true tha:t this epochal work was followed by others; so that the

'Life a11d Letters, II, pp. 366, 367. • Waagen, \Vilhelm Heinrich: "Die Formenreihe des Ammonites

subradiatus," Bcnccke's Geognostische Paliiontologische B eitriige, II, 1868, pp. 185-86.

212 DARvVIN AND P ALEONTOLOGY

ne;v paleontology of evolution, as distinguished from the old paleontology of special creation, reached vast proportions before D arwin's death. But all this remained a terra incogni,ta to D ar­win. Absorbed in his observations on living things, in his vast anthropological, psychological, zoological, and botanical researches in his revision of the Origin and other ,vorks, Dar;vin never found time or opportunity to grasp the meaning of the D arwinian paleontology. H e attempted b~1t failed to understand the ,vork of Alpheus H yatt, ,vhich was directly along the lines of that of W aagen, but unfortunately rendered unneces­sarily n1ysterious and difficult to comprehend through the inveterate American love of ,vord­making. If Hyatt's work had been expressed in D ar,vin's simple language, as it might have been, then D arwin would certainly have grasped the Waagen principle of mutation, and we should have had the benefit of 11is marvelous insight into its significance. As it was, like l\'Ioses, D arwin led his paleontological follo,vers to the Promised Land, but he did not live to enter it; be gave the impulse to search for phyla, or close continuous lines of descent of animals and plants, but he hirnself never observed a single phylu1n.

This simple fact is of vast importance in our estimate of the weight to be attached to D ar­,vin's opinions. In contrast with Herbert Spen­cer he was essentially a deductive-inductive worker; that is, he pursued a trial hypothesis

DAR\<VIN AND PALEONTOLOGY i1s

along the strictest lines of observation, he was less interested in ho,v nature might, should, or would ,vork than in ho,v nature does worlc. Of his trial hypotheses that of adaptation through selection of minute f avorable variations he can­didly tested by all the facts he could bring to­gether; among these, ho,vever, were none of the facts observable only in close phyletic series of fossils. This is a fair ,vay to estimate Dar"vin and to be influenced by him, namely, by his strict inductive methods and in his times, not in ad­vance of his times.

In the last half century thousands of fossil or­ganisms of all kinds have been exactly studied and compared, more or less complete descent series of vertebrates and invertebrates have been garnered, facts and principles entirely unkno,vn to Dar\\rin, and foreign to the logical mind of Huxley as ,vell, have been revealed; in short, the data of induction as to how nature does worlc in the origin of certain new characters have to­tally changed in paleontology perhaps more than in any other biological field of observation.

Tv,10 grand lines of observat ion have been fol­lowed in paleontology quite independently of ea,ch other: first, the minute changes in phyla of invertebrates observed in fossil shells by W aagen, H yatt, Hilgendorf, Neumayr, and many others; second, minute changes in phyla of fossil mam­mals observed by Osborn, Scott, Deperet, M at­the,v, and many others. I t is obvious that the

i14, DARWI N AND P ALEONTOLOGY

hard shells of molluscs and the enameled teeth and other parts of mammals are entirely inde­pendent parts of entirely different organisms, and that if similar la\vs have been discovered in such widely distinct fields of observation they tend to s.how that these laws \vere of force or of wide potency in living organisms in general

We are, therefore, now enjoying an entirely new vintage of facts and principles. Ho\v far can this new ,vine be put into the old bottles of D arwin's beliefs? What would D arwin him­self say if with his incomparable candor and his incomparable power of generalization he were to examine these facts discovered in close phyletic series of vertebrates and invertebrates, and ,vere to test the conclusions which appear to be in­ductively derived from them?

Thus two great questions arise on this anni­versary day in connection with the t,vo words, Darwin and Paleontology: first, \vhat has D ar­win done for paleontology; second, ,..,hat has pa­leontology done for Dar,vin or for the sum and detail of D ar,vin's teachings?

DAR\VIN THE SECOND FOUNDER OF PALEONTOLOGY

The former question is readily answered; as Cuvier was the first, so Dar,vin ·was the second founder of paleontology. His contributions to the principles of the science were prepared for

DARWIN AND PALEONTOLOGY ~15

by his familiarity through Lyell ,vith the "vork of the great Frenchmen Buffon, Lamarck, and Cuvier. These principles " 'ere stin1ulated and made his o,vn by his observations during the voy­age of the B eagle, and his survey of the extinct life of South Ainerica. His comments on " 'hat he sa,v exhibit a close observer of nature, the geologist a.nd biologist, the ideal paleontologist except only in the technical field of anatomy. He himself kne,v f e,v or no lines of descent, but he felt they must be found, and he set the whole world in search for them. 1'hese principles of paleontology ,vere given full expression in the 01igin of Species. There are in that great work innumerable allusions to ,vhat may no,v be called the ,vorking method of paleontology, the method ,vhich Huxley formulated and expressed in clear terms in 1880. Darwin believed that the breaks in the geological record caused the interruptions in the hypothetical phyla, and his ifond confidence that they ,vould be overcome has been more than vindicated. The impulse which he gave to ver­tebrate paleontology ,vas immediate and un­bounded. It found expression especially in the writings of Huxley in England, of Gaudry in France, of l{owalevsky in Russia, of Cope and J\1arsh in America. These works s·wept aside the dry fossil lore ,vhich had been accumulating since the passing of Cuvier's influence, and breathed the new spirit of search for the princi­ples of fitness, of descent, of survival, and of ex-

~16 DARWIN AND P ALEONTOLOGY

tinction. Thus Darwin gave a new birth to pa­leontology, as to every other branch of biology.

The second question, what has paleontology done for Darwin, calls not for one but for a series of ans,:vers. I n son1e ,vays it has vastly strength­ened him as a natural philosopher or as the seeker of natural causes; it affords more convincing proof than any other branch of biology of the truth of D ar,:vin's grandest contribution to our knowledge of the universe, namely, his complete demonstration, which others had attempted and failed to give, of the law of evolution with all its consequences. I n this way it has shown him to be quite in£ allible; in other ,:vays it has under­mined his position and shown him quite as fallible as other great men.

It seems therefore that the most important p art \vhich a paleontologist can play in this dis­cussion is to state exactly and clearly what pale­ontology has to say for and against the special hypotheses set forth by D arwin as ,vell as ,vhat it has to say that is entirely ne"v since D arwin's time.

SELECTION

Dar,:vin's o\vn hypotheses of the causes of evo­lution through Natural Selection are concentric or in ever narrowing circles; they center around the broad surmval of the best fitted groups of organisms of all degrees, of order s, families, genera, species, varieties, of the best fitted single

DARV\TIN AND PALEONTOLOGY ~17

organs, of the best fitted variations in these, and finally come down to the focal point that the causes of adaptation and the origin of species ultimately center around constant variability and the survival or selection of minute variations. From his exhaustive kno,vledge of D ar,vin's "\Vork Professor Poulton holds that the great phi­losopher had in mind as the material for Natural Selection s1nall va1'iations, congenital and inher­itable; he knew well that the 1naterial included "great and sudden variations," but he did not believe that they were selected. His variations had no power of developing in definite direction. Direction was given by Se.lection. That is, it remained for selection to give direction by choos­ing from all variations those which happened to be in an adaptive direction.

It is obvious that as ,ve pass from the broad to the minute the theoretic demand upon the selection hypothesis becomes more and more in­tense, but the tendency of our time is to waive aside theoretic considerations and come down to actual observations and facts and see how far they support the Darwinian and other hypoth­eses, and how far they call for ne,v hypotheses and interpretations.

Thus the question of the hour is to see what parts of this entire hypothetical system of selec­tion within selection, until we reach the minute, :are in accord with modern paleontological evi­dence.

~18 DARWIN AND· P ALEONTOLOGY

Let us begin with ithe broad and proceed to the minute.

Selection of entire ani1nals and parts of ani­mals through elimination. Paleontology not only sustains Darwin's broad induction of evolu­tion, but in an equally convincing manner it sus­tains his broad induction that Natural Selection is and always has been one of the dominant prin­ciples of change in the aspect of the living world. Because of the thousands of facts which he 1nar­shaled from every branch of natural history in support of this factor he is entitled to be regarded as the founder although not as the originator of the law of the survival of the fittest. In study­ing the causes of the extinction of the mammals throughout Cenozoic times, 1 I have been struck by the fact that there is hardly an hypothesis of extinction suggested by more recent research which escaped the more or less serious attention of Dar\vin. My general survey of the economy of extinction in this great class of animals cer­tainly establishes the existence of a very great variety of causes of elimination, some of which are internal, some external in origin, \vhile all operate under the broad principle of selection. I believe I have found fresh proofs of the con­tinuous operation of selection on all 01·gans, be­cause some new and brilliant instances in addi­tion to those gathered by I{owalevsky and lV[arsh

•"The Causes of Extinction of Mammalia," America" Nawralist, Vol. XL, No. 4-79, December, 1906, pp. 769-95; No. 4-80, November, 1906, pp. 829-69.

DARWIN AND PALEONTOLOGY 219

are adduced not only in support of the broad in­duction that the fittest survive, but also in proof of the more specific principle of Darwin that cer­tain single organs, such as certain types of tooth structure, or of foot structure, have been f avor­able or fatal to their possessors. This is now capable of statistical demonst ration and no longer a matter of highly p robable inference, as Dar"•in left it. The most readily comprehended case is that during the Upper Oligocene and Lo,ver Miocene periods, a large number of en­tirely unrelated quadrupeds possessed a closely similar pattern 1 in their grinding teeth; it was the one character ,vhich they possessed in common and certainly was the one character which led them all alike to extinction.

Selection of the larger variations of propor­tion. When ,ve approach the further applica­tion of the selection principle, however, as more novel with Darwin and more intimately asso­ciated ,vith his personal views, namely, his doc­trine of the selection of larger variations of pro­portion, as, for example, in the classic case of the elongation of the neck of the giraffe, we are forced to admit that paleontology neither posi~ tively sustains nor destroys this 'working hypoth­esis, although the evidence ,vhich it presents is rather f avorable than unf avorable.

By exclusion of other hypotheses, paleontol-1 I allude to the grinding teeth technicallly known as bunosele­

nodont, that is, with a. rounded crown ( buno.s) on the inner side of the grinders, .and crescentic (se/erni) ridges on the outer side.

~~O D AR \VIN AND PALEONTOLOGY

ogy may ho"½-·ever be said to lend support to this hypothesis. Changes of proportion in long periods of time, that is, in millions of years, play an enormous part in evolution, as seen by the fol­lo,ving contrasts in certain ,Yell-known structures, among herbivorous quadrupeds :-

Short-toothed and long-toothed=short-lived and long­lived.

Short-toothed and long-toothed=browsers and grazers. Short-footed and long-footed =short rangers and

long rangers. Short-headed and long-headed =browsers and grazers. Short-necked and long-necked =near feeders and far

f ee<le1·s.

Among the horses these very changes of pro­portion in four impo1tant organs, the teeth, the feet, the head, and the neck, constitute a very large percentage of the total evolutionary changes, and result fina.lly in certain phyla of horses becoming long,lived animals, capable of traveling long distances, capable of grazing on the harder kinds of food, and capable of reach­ing food at a considerable distance from the body. T his joint action of heredity, ontogeny, environment, and selection of congenital varia­tions of proportion, appears to best explain the t ransformation of round-headed or brachyceph­alic into the long-headed or dolichocephalic forn1s of the horses as well as of other herbivora, in re­lation to the bro,vsing or grazing habit respect­ively. T he only explanation ,vhich has as yet

DARWIN AND PALEONTOLOGY ~~l

been offered for such changes 0£ proportion is that of the selection of hei-editary quantitative varia tions.1

I am therefore myself inclined to regard long­headedness or short-headedness in the vertebrates generally as well as the si1nilar phenon1ena of long-footedness ( dolichopody) or short~f ooted­ness (brachypody) as in many cases caused by the selection of changes of proportion; yet I freely admit that " 'e can not prove or demonstrate this Darwinian hypothesis through paleontology.

One direct paleontologic:al reason may, ho·w­ever, be adduced in favor of the hypothesis of selection of variations of proportion, namely, changes of proportion do not fall under ·what I call the la,v of ancestral control of variation. H ead proportions or foot proportions, or, in fact, any other change of proportion can not be regarded as controlled by ancestral affinity, be­cause descendants of the san1e ancestors soon give rise to very different results. For example, a priinitive intermediate ( or mesaticephalic) form of skull does not at all control the form of skull which may be derived from it; the animal is free, as it ,vere, to evolve into one of many different kinds of head forms. The point is that hered­itary predete1·1nination does not appear in the evolution of proportion and of for1n as I shall sho"v that it does appear in the evolution of cer-

, The fact that this throws little light on the origin of dolicho­cephaly or brachycephaly in the human species appears to throw the selection hypothesis again into doubt.

!2!2!2 D.ARWIN AND PALEONTOLOGY

tain other new characters, except in so far as an evolutionary tendency once established in the direction of brachycephaly or dolichocephaly is apt to be pursued to its very limits or extremes.

Selection of miniite variations. Not only is paleontology not positively conclusive on the hy­pothesis of selection of large variations, it has nothing positive, but rather something negative to say on the still more intimate or focal feature of the Dar,vinian hypothesis that minute varia­tions wi,thoitt direction in certain specific organs are of survival or of eli1nination value. Certainly appeal must be made to some other branch of biology on this particular problem, if indeed it is ever capable either of verification or of dis­proof. Through paleontology we can neither say that Dar"vin was right or wrong, because ,ve meet with certain peculiar barriers or limitations of paleontological observation. Slight changes of geological level may n1ark long periods of time. The limitations :are not solely due to rela­tive rarity of conte111poraneous or synchronous material, because a111ong invertebrates vast nun1-bers of synchronous f or111s are son1etimes brought together so that n1inute variations may be read­ily measured, but it is quite a,nothe1· matter to prove through paJeontology that such variations are selected. I t was ,v aagen's vie\:v that it is not the variations but the less conspicuous 1n'1tta­tions which reappear in the next generation. This question of the s-election of nnnute varia-

DAR\V-I N AND PALEONTOLOGY ~~3

tions is probably par excellence a field of research for the biometrician and the experimentalist rather than for the paleontologist.

ORIGI N OF NE\1/ CHARACTERS

v,r e no,v reach a turning point and pass from differences of proportion, of development, and of degeneration, to the origin of ne,v chaTacters.

Origin of new characters not by selection of the fit from the fortuitoiis. , i\Then, however, this focal point of the selection of minute var iations is pressed home as an hypothesis of the origin of all new adaptive characters, then paleontology ceases to be either neutral, silent, or inconclusive, and gives to Darwinism a most emphatic nega­tive. I n all the research since 1869 on the trans­formations observed in closely successive phyletic series no evidence whatever, to my kno,vledge, has been brought for-ward by any paleontologist, either of the vertebrated or invertebrated ani­mals, that the fit originates by selection from the fortuitous.

L est the statement be made that this is truly the sanct11,1n sanctorwm of D ar,vin's theory of adaptation, let me recall the historical fact 1 that fitness for t,venty-five centuries had been the stumbling block of those ,vho sought a natural­istic interpretation of nature; that l(ant O had

' Osborn, H. F. : From tlte Greeka to Darwin. An Outline of the Development of the Evolution Idea, Vol. 1 of the Columbia University Biological Series, Svo, l\'.lacmillan, Srcl eel., p. 248.

• l bid, p. 100.

9l9l4 DARWIN AND P ALEONTOLOGY

wondered if any one could ever give an explana­tion of the origin of fitness in a blade of grass; that fitness had become the teleological citadel of the supernaturalists. Dar,vin ,vas believed by many, but not by all, to have solved this problem of the ages. Let me quote the very 1·ecent lan­guage of our most profound American philo­sophical thinker, W illiam J ames 1

:-

" It is strange, considering how unanimously our ancestors felt the force of this argument [ that is, the teleological], to see how little it counts for since the triumph of the Darwinian theory. Darwin opened our minds to the power of chance-happenings to bring forth 'fit ' results, if only they have time to add themselves together. He showed the enormous waste of nature in producing results that get destroyed because of their unfitness."

I repeat : paleontology is not silent, but pre­sents a solid array of evidence against what ,vas never moire than an ingenious working hypoth­esis of D arwin; one he fathered and loved, it is true, but ,vhich met little favor in the sturdy and logical mind of Huxley, predisposed as he ,vas to Dar1,vinism. I t is no,v no longer a question

1 James, William: P,·agmatism. Svo, Longmans, Green & Co., New York, 1907, pp. 110, 111. Professor ,vuuam Bateson gives a similar definition. "Darwin's Solution. Darwin, without suggesting causes of Variation, points out that since (1) Varia­tions occur-which they are known to clo-ancl since (g) some of the Variations are in the direction of adaptation aod 0U1ers are not- which is a necessity- it will result from the conditions of the Struggle for Existence that those better adapted will on tl,e whole persist and the Jess adapted will on the whole be los~." Materi«ls fo•· U,e Study of Variation, T·1·eated with Espec,at Regard to Disco,./.i,.uity ;,. tl,9 Origin of Species, Svo, London, 1894-, p. 5.

DARWIN AND P ALEONTOLOGY ~~5

of logic but of £act. Does paleontology sup­port this focal hypothesis of fortuity or absence of direction i111 the minute variations lea,ding to adaptation, 01· does it destroy it?

The ans,ver is in no uncertain sound. While fortifying all the out,vorks, paleontology under­mines the hypothesis of adaptation through the selection of the rurected from the variations ,vith­out direction by eliminating the occurrence of the variations wi,thoid direction in many important organs. Fortuitous variations as material for advance should certainly be found, if anywhere, in closely successive phyletic series; they have not been found. At the same time this evidence does not leave a vacuum, but replaces the law of chance by another law, na1nely, that as in the domain of inorganic nature, so in the do1nain of organic natu1·e fortuity is wanting, and the fit originates in many hard parts of the body through la,vs ·which are in the main similar to gro,vth,-la ,vs the modes of ,vhich ,ve see and measure, the causes of ,vhich ,ve do not and may never understand, but nevertheless la"'S and not fortuities or chance happenings.

N o,v let us inquire ho,v it comes that paleon­tologists, far in advance of other biologists, have reached this profoundly important principle as to the origin of certain ne,v characters.

The paleontologist observes origins. Having already disclaimed certain powers for paleontol­ogy as regards evidence on the evolution factors,

226 DARWIN AND P ALEONTOLOGY

and having still others to disclaim, I may now claim for paleontology as its transcendent power that it alone of the biological sciences can pro­duce evidence of the reign of definiteness, of order, of law in the origin and early history of certain adaptive characters, because in the hard parts of animals it alone is in with organs before their beginnings and from their beginnings to their finalities. The beginning of ne", charac­ters is at once the central problem and the most mysterious problem of evolution. I n using the word " beginnings " or " origins " we do not imply causes but simply appearances in order of time. It is of unique advantage to the paleon­tologist as an observer of the origin of new char­acters that concentrating his attention on single characters entirely irrespective of the species question, 1-vhich is ·wholly a by-question, he may trace ne,v characters from the period before their origin, through their first adumbrations, thl·ough the stages ·which may be denominated as origins. through their every subsequent change, through their entire history, in fact. In this long-lived sense as an observer the paleontologist is immor­tal in contrast ·with those mortal observers, the zoologists and experimentalists.

Second, in successive series of animals such as horses, rhinoceroses, or the related titanotheres, the paleontologist may observe the belhavior of a very large number of characters at the same time and through long periods of time, some rising,

DARWIN AND PALEONTOLOGY 227

some falling, one structure taking a rounded form, the structure next it taking a crescentic form, every single element evolving independ­ently in some ,vay. T he theory of the simulta­neous operation of several factors on different groups of characters and on different kinds of group characters could only suggest itself to a paleontologist working on a very complex ani­mal like one of these big quadrupeds in ,vhich countless numbers of chai-acters are simulta­neously evolving.

T hird, the paleontologist has this further unique advantage: he is in a position to judge which new characters are important and which are unimportant; he is, therefore, in a peculiarly f avored judicial position. By contrast neither the zoologist nor the botanist is in a position to know ·whether a ne,v character ,vhich he believes to be important is going to persist or not. T he difficulty under which the zoologist labors in this lack of judicial discernment is illustrated, for instance, in Bateson's Materials for the Study of V ariation, in ,vhich he attempts to prove the la,v of discontinuity from a revie,v of a very large assemblage of characters, the greater number of which the paleontologist would recognize at once as vvholly unimportant and non-significant. T he only way zoology and botany could overcome this disadvant age, as regards the origin of ne,v characters, would be t hrough a series of relay observations extended by successive observers

228 DARWIN AND PALEONTOLOGY

over long periods of time or thxough a series of lifetimes. The mortality of the zoologist, the experimentalist, the botanist, is a fatal handicap, for the reason that they are alike too short-lived to observe and measure those changes in the hard parts (if they exist) which are so excessively slow· as to be invisible and immeasurable by mortal eye; while the paleontologist alone is in a posi­tion to demonstrate the existence and importance of such slow origins. With his short-time vision is not the zoologist and botanist more prone to fall into the error of "exclusive hypotheses," and conclude that visible, measurable changes, such as saltations, discontinuities, mutations· of De Vries are the most important if not the only changes which are going on in organisms? Thus the paleontologist listens serenely to the fanfare of trumpets of exclusive hypotheses; he kno,vs that time and time alone "~11 sho,v ,vhether these will ,vith other fashions fade.

Siidden origins de1nonstrable by zoology and botany, but not by paleontology. As regards the soft parts of animals and even as regards pro­portions, changes " 'hich occur geographically or in space can be measured by the zoologist, but this does not apply to origins. The first point as to origiin, namely, the question of rate or speed of origin, finds paleontology at a disadvantage as a sphere of research. The la,v of sudden or discontinuous principles has repeatedly been demonstrated in zoology and in botany. I t

DARvVIN AND PALEONTOLOGY ii9

reaches the cli1nax in De Vries' work, where mu­tation is regarded as an exclusive principle, but discontinuity .can never be either demonstrated or disproved by paleontology, since this is the most unfavorable of all the biological fields for the recognition of sudden changes of character, through absence of that abundance of synchro­nous and contemporaneous material f OT com­parison on " 'hich alone it is safe to establish the existence of a mutation. Despite this obvious shortcorning of paleontology, it is noteworthy that the saltatory hypothesis has been- illogically I believe- fathered by a series of paleontologists, by St. Hilaire in 1830, by Cope, and more re­cently by D ollo and Smith Woodward. I t should be borne in mind constantly that wherever a ne,v animal suddenly appears or a new char­acter suddenly arises in a fossil horizon, such ap­pearance may be attributable to the non-discovery of the greater or more minute transitional links ,vith older forms or to the sudden migration of a new type provided with a ne"v organ or organs which have g1·adually evolved else,vhere. }Y[ore­over, the doctrine of sudden appearances is di­rectly the reverse of Waagen's la,v of mutation. The point, ho,vever, is that as a sphere of evidence paleontology neither approves nor disproves the law of discontinuity.

Slow origins demonstrable by paleontology, but not by botany or zoology. Paleontology, on the other hand, affords the most favored field for

230 DARWIN AND P ALEONTOLOGY

the observation of slow origins of new characters. It is well known that Darwin was a firm advo­cate of the hypothesis of slow origins; this was, indeed, consistent with his doctrine of evolution by the adding up of favorable fluctuations. The law of gradual appearance or origin of many new characters in definite or determinate directions from the very beginning I regard as the grandest contribution which paleontology has made to evolution. This law of gradual change in the origin and development of single characters, measurable only at long intervals of time, has now come to rest on a vast number of observa­tions; it is the working basis of the science. Ver­tebrate and invertebrate paleontologists search­ing independently of each other on wholly differ­ent kinds of animals have reached entirely sim­ilar opinions.

Mutations of W aagen. The first , I believe, to express from observation the la,v of gradual change was Waagen in 1868. The mutations of Waagen 1 ,vere originally distinguished by him from the often more conspicuous contempo­rary fluctuations by the fact that, although seen in minute features, they are very constant and can always be recognized again, but only in success­ive geological levels, that is, at intervals of n1any geologic years. Such gradations are observed

' \Vaagen, \Vilhelm Heinrich: ";l)ie Forn~enreihe ?es Amn'.on_ites subradiatus," Be1tecke's Geognost,sche Palaontolog,sclie Be,tr11ge, 11, 1868, pp. 185-86.

DARWIN AND P ALEONTOLOGY 231

in single characters; they are the nitances, or shades of difference, ,vhich are the more gtadual the n1ore finely we dissect the geologic column; bit by bit the W aagen mutations are added to each other in different single characters until the sum or degree of mutations is reached which no zoologist ,vould hesitate to assign specific or ge­neric rank. The essence of Waagen's mutation is orthogenesis or variation in deter1ninate direc­tions, as distinguished from the indefinite varia­tion implied in Dar,vin's theory.1 This law re­ceived the powerful support of our countryman Hyatt, of the Austrian paleontologist N eumayr, and many others.

I n 1889 Osborn,2 in observing the teeth of large numbers of Eocene mammals, chiefly of the smaller monkeys, horses, tapirs, and other forms, :first noticed that new elements here also arise def­initely and can only be measured after long in­tervals of time. He first applied (1890) the term " definite variations " 2 to these characters, but many years later, on observing that many such characters were destined to become adaptive, he gave the same elements the name " rectigrada-

' Professor Poulton maintains that determinate vairiation is precisely what Natural Selection would show, namely direction through the accumulation of favorable variations.

' Osborn, H. F.: "The Paleontological Evidence for the Trans­mission of Acquired Characters," British Associatio" Reports, Newcastle-upon-Tyne meeting, September, 1889. London, 1890.

•"Are Acquired Variations Inherited? Opening a Discussion upon the Lamarckian Principle in Evolution." American Society of Naturalists, Boston, December 31, 1890. American Naturalist, Vol. XXV, No. 291, i\farch, 1891, pp. 191-216.

~Sfl DARWIN AND PALEONTOLOGY

tions." 1 It appears probable, but it is not yet demonstrated, that the rectigradations of Osborn are of the same nature as the mutations of ,v aagen. Scott 2 in 1894 ,vas the first vertebrate paleontologist to call the attention of his co­,vorkers to ,i\r aagen's la,v among the inverte­brates. This principle of rectigradation in the origin of many new characters in the mammals cuts both ways; it demonstrates the absence of the chance happenings without direction, ,vhich forn1 the basis of Darwin's hypothesis of the origin of adaptations, and positively shows that certain new adaptive characters appear definitely and assume adaptive direction £ rom their very minutest beginnings.

To sum up, the la,v of gradual change in cer­tain determinate, definite, and at least in some cases adaptive directions, through very long periods of time, and the absence of chance or non­direction in the origin of a large number of adaptive and other new characters, is the com­mon working principle both in vertebrate and invertebrate paleontology.

It is thus that the characters which the older paleontological observers, such as O,ven, Leidy, Cope, and Marsh, designated as specific and even as generic are gradually built up. VVe thus ,vit-

• " Homoplasy as a Law of Latent or Potential Homology," America" Nal!t.,-alist, Vol. XXXVI, April, 190!l, pp. !!59-71.

' Scott, \V. B.: "On Varitttions and ll'lutations," America•• Jo11rr1al of Science, Vol. XLYIII, 189-l, pp. 355.7.i.

DARWIN AND PALEONTOLOGY fi8S

ness the origin of ~vhat naturalists have been des­ignating as species.

In a lo,ver borizon a cusp of one of the teeth, for example, is adumbrated in shado,vy form; in a slightly higher horizon it is visible; in a still higher horizon it is fully grown, and all paleon­tologists have hitherto agreed to honor this final stage by assigning to the animal which bears it a ne,v specific nan1e. In the face of these con­tinuous series of changes revealed by paleontol­ogy the species and genera of L innreus break up into the continuous chain of the "mutations of l i\T aagen," and for such progressive changes Deperet has proposed the term " ascending mu­tation."

~ 7 o theoretical confiict between the rnutations of Waagen and of D e V ries. It will be sho·wn presently that a very considerable number, if not all, of these slo,v origins are of a kind which arise from internal causes ( intrinsic causes, ,i\Tilliams), that is, in heredity. It is evident that if there do exist hereditary predispositions to mutate in def­inite directions, such predispositions may mani­fest themselves very gradually, as in the " muta­tions of ,,, aagen," or under certain circu1n­stances very suddenly, as in the lesser saltations or "mutations of De Vries." Theoretically, at Least, there thus ceases to be any inherent conflict between the hypotheses of " continuity " and " discontinuity "; the latter may represent an in­tensified or accelerated state of the former.

~34 DARWIN AND PALEONTOLOGY

ADAPTATION

Adaptive natiire of certain new origins. Dar­,vin's hypothesis of the selection of variations lacking direction is essentially a la,v of chance. Origins of many kinds and in many places should be observed; the principle of trial and error should be seen in operation; paleontology should be an especially favorable field for such observation. Yet, as noted above, the mutation la"' of \¥ aagen and the identical or similar rec­tigradation la,v of Osborn is essentially a prin­ciple of definiteness and determinateness from the beginning.

D efiniteness is not necessarily adaptiveness. The novel feature of Osborn's observations in 1889 on the cusps of the teeth appears to consist in the demonstration of this element of adaptive­ness; 1 the ne\v element is not merely determi­nate, but it is leading directly to utility, and will at a late1· stage be useful. Thus vertebrate pale­ontology enables us to establish the law that cer­tain origins are adaptive in direction fro1n the beginning; namely, the la,v of rectigradation.

Such origins of new characters are chiefly 1ii,1,rnerical; s01nething is added to the organ or to the organism which did not exist before in vis-

1 "Certain Principles of Progressively Adaptive Variation Observed in Fossil Series." Biological Section of the British Asso­ciation for the Advancement of Science, British .&ssociatio,. Re1>0,-ts, 1894, p. 643 (title); Nature, Vol. 50, No. Hl96, August, 30, 1894, p. 495.

DAR,VIN AND P ALEONTOLOGY 235

ible f orrn, such as the beginning of a cusp or of a horn. 'l'he origin of horns has al,vays been a famous problen1, because horns are eminently in the nature of new characters. In the great quad­rupeds kno,vn as titanotheres rudi1nents of horns first arise independently at certain definite parts of the skull; they arise at first alike in both sexes, or asexually; then they beco1ne sexual, or chiefly characteristic of 1nales; then they rapidly evolve in the males while being arrested in development in the fe1nales; finally they become in some of these anin1als do1ninant characters to ,vhich all others bend.

T he form, the proportion, the n1odeling, both of the cusps and of the horns, accord ,vith the proportions of the teeth or of the skulls in which they appear; they are thus correlated in form ,vith other organs. The cusps of the grinding teeth of n1ammals form a peculiarly advanta­geous field of observation because they do not depend either upon ontogeny or environment for their perfection; they are born complete and per­fect, use and environment destroy rather than . . perfect them. They thus contrast ,\•ith the bones, muscles, and many other tissues of the body ,vhich depend upon ontogeny for their per­fection.

Failure of atte1npted explanation of adaptive origins by trans1nission of acquired characters. I n seeking explanation of .. this definiteness or adaptiveness of direction in the origin of certain

~36 DARV\!IN AND PALEONTOLOGY

new parts, it ,vas natural to first have recourse to the doctrine of the transmission of acquired char­acters, because it is a ,:vell-known principle that certain organs are definitely directed or guided along adaptive lines by use. By reference to my papers of 1889 and 1890, it ,vill be seen that it was in seeking an explanation of direction, I ·was led to support the Lamarckian principle. I do not propose to discuss this enormous question here. Cope concentrated his ,vhole energy on trying to demonstrate Lamarckianism from pa­leontology, but ended in a logical fai lure, or non sequitur, because the explanation ,vill not apply to all cases. Here again I believe that experi­mental zoology rather than paleontology is the best field of research, and that the La1narckian principle should not be finally abandoned until it is tested by a prolonged series of experin1ents extending over many years. It is ,vell kno"·n that Dar-\.vin, for the very reason that he thought he sa"v in it a " 'orking explanation of a directing influence on heredity, finally adopted the La­marckian principle and proposed his hypothesis of pangenesis. This ,vas also the ground of n1y first conclusion of 1889, yet o,ving in the first instance to a trenchant criticis1n by Poulton, I have for the time abandoned this La1narckian interpretation, since quite apart fro1n the difficul­ties in the field of heredity, paleontology appears to offer many objections to it. The objections are simply these: that a very large number of

DARvVJlN AND PALEONT OLOGY ~37

ne"', de.finite, orthogenetic characters ,vhich could not have been acquired in ontogeny arise at birth, among then1 the cusps of the teeth. Since the Lan1arckian doctrine either fails or need not be iinvoked to explain these de.finite adaptive origins iin the teeth, and apparently also in the horns, ,vhy invoke it for other adaptive phenomena? This does not preclude the constant operation of t he law of organic selection 1 or the " selection of coincident variations" advocated by l\1organ, Bald,vin, and myself, which I still regard as a useful supplementary hypothesis to Natural Se­lection, explaining many of the alleged instances of the inheritance of acquired characters.

Unknown causes of certain adaptive origins. I n 1890 I pointed out that, since the La1narckian p rinciple gave us a ,vorking hypothesis of direc­tion in these adaptive origins, in abandoning the L amarckian principle ,ve would be left ,vithout any explanation, and in developing this idea I ca1ne to the conclusion in 1895 ~ that we must appeal to the existence of some unknown factor

' Osborn H. F .: "A Mode of Evolution Requiring Neither IS'atural Selection nor the Inheritance of Acquired Clharacters (Organic Selection)," Tra11s. N. Y. A cad. Sci., March and April, 1896, pp. 141-48.

See also: "Ontogenic and Phylogenic Variation," Science, Vol. IV, 1896, l\"ovember 27, pp. 786-90; "Organic Selection," Science, N. S., Vol. VI, No. 146, October 15, 1897, pp. 583-87; •· The Limits of Organic Selection," American Naturalist, Vol. XXI, November, 18V7, pp. 944-51; ":Modjfication and Variation, and the Limits of Organic Selection: A Joint Discussion with l'rofessor Edward JB. Poulton of vxford University," Proc. Ame,·. Assoc. Ado. Sci8nce, Vol. 46, 1897, p. :!39.

•" The Hereditary Mechaojsm and the Search for the Unknown Fa~tors of Evolution," Biol. Leet. Ma.-ine Biol. Lab. 1894, Ginn & Co., Boston, 1895.

238 DARWIN AND PALEONT OLOGY

or factors of evolution. Subsequent research has convinced me that in these phenomena of the internal origin first of certain determinate char­acters, and second of certain adaptive charac­ters, ,ve are dealing with the unkno,vn if not ,vith the unkno-,,vable, although the latter despairing attitude should not be hastily adopted. The immediate causes are internal, that is, they lie in the domain of heredity rather than of ontogeny, environment, or selection; but lest I might be mistaken on this point, I have devoted several years of thought to the development of a circle of causes, so to speak, which I have finally formu­lated ' in the la,v called the foi~r insezJarable fac­tors of evolidion. According to this la,v I re­gard heredity not as something inseparable, al­though extraordinarily stable; on the contrary I have recently expressed the relations of heredity to the other factors as follo\vs :-

The life and evolidion of orga11is1ns contin­uously center around the processes which ·we term heredity, ontogeny, enviro1i1nent, and se­lection; these have been inseparable and inter­,acting fro1n the beginning; a change introduced or initiated through any one of these factors .causes a change in all. First, that 1,vhile insep­arable fro111, the others, each vrocess 1nay in cer-

• The Four Inseparable Factors of Evolution. Theo_ry of Their Distinct and Combined Action in the Tra11sformahon of the Titanotheres, nn Extinct Family of Hoofed Animals in tile Order Perissodactyla," Science, N. S., Vol. XXVII, No. 6S:!, January !14, 190$, pp. 148-50.

DARWIN AND P ALEONTOLOGY 239

tain conditions becorne an initiative or leading factor; second, that in cornplex organis1ns one factor 1nay at the sarne ti?ne be initiative to an­other group of characters, the inseparable action bringing about a continuously harmonious result.

This inseparableness of internal processes (he­redity and ontogeny) and external processes ( selection and environment) is not surprising ,vhen ,ve reflect that it n1ust have existed from the very beginnings of the organic ·world.

Thus hypothetically the origins of certain ne,v characters in heredity may find expression not spontaneously, or irrespectiYe of conditions, or fro1n self-operating internal mechanical causes, but through some unknown and at present en­t irely inconceivable relation bet,veen heredity ( the germ-cells), ontogeny or habit and use ( the somatic cells), environment or external condi­tions, and selection. This does not preclude spontaneous origins.

Prolonged analysis and synthesis of the evolu­tion processes of the various kinds ,vhich led to the enunciation of the above la,v only served to convince me that certain adaptive origins are im­mediately matters of heredity ,vhatever their in­iitiation may be in the circle of ontogeuetic or environ1nental causes. vV e have to do ,vith a JJotential of similar mutations or rectigradations independently.

Here ,ve find ourselves expanding a principle which was clearly foreshadowed by D ar,vin, and

i40 DARWIN AND PALEONTOLOGY

which, had he pursued it to its logical sequence, would have brought him to orthogenesis, namely, that variations may not be ,vithout direction, but that law may lie among the hidden recesses of the nature of the organism; in other words, Dar,vin himself frequently professed ignorance of the la,vs of variation as well as the belief that such laws might be discovered. P aleontology has revealed certain la,vs of variation, and it is quite con­sistent with the principle that the ancestral nature of the organism limits and conditions variation that I have to record the following interpretation or hypothesis 1 announced in 1902, namely, that the adaptive 01igins of certain characters are predetermined by hereditary kinship. This pre­determination may be due to a similarity of hereditary potential in evolution, that is, ani­mals of similar kinship transmit similar poten­tialities in the origin of new characters. There is an ordinal kinship, a family kinship, a generic kinship, etc. T his first renders possible the oc­currence of certain ne,v characters, and second, conditions or limits these ne,v characters ,vhen they do occur. For example, in a certain inde­pendent series of extinct anin1als derived from common ancestors, we can predict ,vhere a new, cusp or a new horn rudiment ·will show itself be-

' Osborn, H. F . : " Homoplasy as a Law of Latent or Potential Homology," American Nat,ural-ist, Vol. XXXVI, April, 19rul, pp. 259-71.

The term rlomoplasy was wrongly employed in t11is paper under a misapprehension as to the significance which its author, Pro­fessor E. Ray Lankester, intended to apply to it.

DARWIN AND PALEONTOLOGY ~41

fore the actual occurrence of either. It is only through some such restraining or li1niting law of hereditary kinship and potential that we can explain the marvelous uniformity ,vhich exists, for example, in the fundamental structure of the grinding teeth of the mammalia.

H ypothetical interpretation. This is not to be understood as an internal perfecting tendency. Such an interp1·etation may be abandoned a.t once so far as it applies to the independence of these hereditary origins from other causes. W hile a phenomenon of heredity, the definite origin of adaptive structures is, in a manner ,vhich is en­tirely inco1nprehensible to us, related to ontogeny and environment, to new habits and new condi­tions of life, there is a marvelous nexus be­t,veen the internal and the external. T hus, for example, if a monkey or lemur begins to imitate the ha.bits of the hoofed animals by beco1ning herbivorous, it also begins to acquire the dental cusps of the herbivorous hoofed animals in ap­proximately the same order. This principle of the relation of the internal and the external lies at the basis of many of the phenomena of par­allelism. For example, some of the Eocene monkeys so closely parallel the Eocene hoofed mammals in dental structure that they were first placed in the same taxonomic order. Some un­known relation between external and internal causes appears to evoke the potential of similar development. Thus there appear to be accelera-

~4~ DARWIN AND PALEONTOLOGY

tions and retardations of characters in heredity which remind us of the well understood laws of acceleration and retardation in individual de­velopment.

D egrees of kinship also affect to a certain ex­tent, but not absolutely, the time of appearance or the time of origin of new characters as \veil as the rate of their development. Thus four lines of Eocene quadrupeds (Titanotheres) branched off independently from one stock; in all the branches \Ve observe similar new cusps arising on the premolar grinding teeth, and similar new horn rudiments rising on the forehead above the eyes, both independently evolved. Neither the ne,v cusps nor the new hornlets appear at just the same n1oment of geological time; some phyla hasten forward these rectigradations, other phyla retard the1n.

The in.dependence of single characters and multiplicity of origins. T he independence of single characters reminds us of the independence of the " unit characters " as kno,vn to the stu­dents of Mendelism and of De Vries' mutation, yet the single characters ,ve have in mind are not unit characters in the Mendelian sense because they do not n1endelize; they appear in every indi­vidual. The independence of single characters in the " W aagen mutations " or the " Osborn rectigradations " is sho"'n by the fact that a con­siderable number of characters evolve in a per­fectly regular and la,vful succession. Each char-

DARWIN AND PALEONTOLOGY fl43

acter is a la,v unto itself, yet all subserve the gen­eral good. For example, a ne,v horn rudiment arising on a brachycephalic skull "''ill be broad or rounded; if it arises on a dolichocephalic skull it will be elongat e or oval. Thus in a large quad­l"Uped like a horse, a tapir, :a titanothere, or a rhinoceros each horn, each tooth, each bone of the skull and skeleton, and by inference all the hard parts as ,vell as all the so£ t parts of these animals in each phylun1, have tv;o sets of relations:

I. In the origin of ne,v characters each phylum ,v:ill evolve, like other phyla, hypothetically through inherited predispositions. T hus from forty to forty-eight ne,v characters ,vill similarly al!:ise in a number of phyla in the grinding teeth alone.

II. In changes of proportion and in rate of evolution each phylum will evolve unlike other phyla, through freedom fron1 hereditary predis­position in matters of form, proportion, and rate of evolution.

These are the conclusions which I have reached after t,,·enty-t,vo years of very precise ,vork on the evolution of the mammals. Besides exactly observing primates, horses, rlhinoceroses, during the past seyen years I have devoted myself to still more precise monographic ,vork on the group of titanotheres, bringing together great quanti­ties of material, and ,vith the assistance of l\Ir. \V. I{. Gregory making thousands of exact ob-

244 DARWIN AND PALEONTOLOGY

servations and measurements. Thus the evo­lution of the group has been traced from a small, hornless animal, of the size of a sheep, to a gigantic horned quadruped little inferior to an elephant. I have realized that the origin of all changes ·which are discovered in the skeleton must be credited to one of the four factors ·which take part in evolution, namely:-

H EREDITY.

ONTOGENY.

ENVIIRONMENT.

SELEC'l'ION.

T hus ne"v characters which can not be credited immediately to selection, to ontogeny, to environ­ment, must by exclusion be attributed to heredity, these are the mutations or rectigradations.

:METHOD OF EVOLUTION (TITANOTHERlES)

An interpretation of the evolution of a family. In picturing the evolution of this great famliy of quadrupeds, the titanotheres, through a long period of time and ,vith an unique sequence of material, may ""e not interpret the facts by imag­ining a continuous interoperation of the four chief factors, and analyze ,vhat we see somewhat as f ollo,vs?

First, these animals are all of the titanothere kinship and of the larger perissoclactyl kinship. The ordinal kinship and the f an1ily consanguinity

f>L.\. TE V.

A.

B

HECTIC lUO.ITIOXS IX TIIE TEETII 01<" EOCEXE l.iXGUl,ATES .

. \. ;\ J)rimitivc Ec1111d. Oroltitwns Ill). B. A ;>ruuitin: T1ta11otlu.:rv, l'<rl<Ct~!JOJJS pal1ulos11s.

From ~J)ecirueu:! iu the .American .Mui;cum ~,r N1uurnl IJi~tory. [ntcrnnl \'iCW or lower h.:t<t11,

Tht: circk~ m/\rk 1he cuep.: whicll llPPC:ll' indC'J)CtHlcnrly 111 1he diffe:retH phyla : thty :ire :lt tlr::-t. 1,arely dt-il>li: bul iucn:a~e in ::-i.-.e iu ~u<:ce~:;1,·e ~colo~i1t.,1I levels.

&'r ~ , : ~ ··1 i ..

'.,

I, ' 'f

' t '\

C

'l'oP Vu;;w OP T11ni::1,: Sr-ur.1,s 0 1-' EocE:-:1:: TrrANOTHEIIES Il,UJS-ru.1-r1NG

B11., cll,CEPU.\I, Y, :llESATICEPII ,\ ~y, ANO DoucaOCEPllALY H1;;SPECT­

[ \fl!:L 'i.

(From ~pccimcns in the Amtricun Mu.Fenm or Ntllurnl Jli!litory.)

A. Pal<€0S!J0/>8 uw)or. brochyceplwlic. B. Jfa,1tcocd{(6 11wn(Mce,,,~. ll)t:'f1HICOJ)httlic.

c. lJQllc/iQ1ltitlll$ COrtWl/1$, dolichoccpholic':.

DARWIN AND P ALEONT0L0GY 245

(different from that of the tapirs, rhinoceroses, or horses) apparently tincture and condition many things ,vhich happen in the evolution of this group. There are forty-four grinding teeth altogether; t,vel ve of these teeth ( the molars) early attain their final form, but are destined through family kinship to lose certain characters and to change their proportions through generic kinship; t,velve others (the premolars) have not attained their final form, but gradually do so through the origin of from forty to forty-eight ne,v characters, each of which appears to arise through an unkno,vn la,v of hereditary predispo­sition, ,vhich operates alike, through ordinal kin­ship, not only in the titanothe1·es but in all other odd-toed or perissodactyl mammals to ,vhich the titanotheres are related. Changes of proportion in the skull, ,vhether to"1ard breadth (brachy­cephaly), or to,vard length ( dolichocephaly) , af­fect the form of the grinders as a whole and thus the birth-form o:f each of these ne,v cusps. The immediate cause of changes of proportion is not interpreted as due to hereditary predisposition, because in teeth, in skull, in foot and li1nb, and even in horns each generic bran.eh or phylum from the original stem forms of titanotheres acquires its o,vn proportions. Thus changes of proportion are interpreted rather as immediately affected by ontogeny, by the mechanics of use and disuse, by. an environment which f avors some rather than other proportions, but especially by the selection

'

246 DARWIN AND P ALEONTOLOGY

of variations in proportion which coincide with the needs of the phylum.1

No abrupt variations (mutations) have been observed in the evolution of the titanotheres, but this in no way renders it inconceivable that skel­etal mutations in the De Vries sense have pro­duced new races in certain phyla. The addition or loss of a vertebra in the sacral region, which appears to distinguish certain titanothere phyla, may be a case of such sudden inheritable muta­tions.

Independently in four or five Eocene branches of the titanothere stoc1{ the horn rudiments very gradually arise, apparently through hereditary predisposition or family kinship, as rectigrada­tions, at the junction of the nasal and frontal bones. As in the case of the cusps, the shape of these horn rudiments is from the first conditioned by the respective breadth (brachycephaly) or length ( dolichocephaJy) of the skull.

The branches or sub-phyla become more and more sharply distinguished from each other by increasing brachycephaly or dolichocephaly, brachypody or dolichopody, apparently thi-ough congenital variations of proportion accumulated by selection and guided by ontogeny through '' organic selection." The anunals belonging to

• It is important to note, on the authority of Professor Castle, that proportions of the skeleton and probably of the teeth arc ''.ot inherited as distinct "unit characters.'' Inbentamce of bone size and shape seems to be as a rl!lle regularly blended by interbreed­ing and wit11out subsequent Mendclian splitting .

•

DARWIN AND PALEONTOLOGY 247

these branches appear to have chosen theill.· own local enviro1unents, ·whether in localities f avor­able to grazing or to bro,vsing, and in turn con­genital changes of proportion would be f avored by selection if in the right direction. The trans­f orn1ation into brachycephaly and dolichocephaly is brought about through independent changes of proportion in every bone of the skull, as ascer­tained by exact comparative measurements. A trend once established in either direction seems to constitute a sort of "hereditary momentum" or predisposition, which leads to great extremes of brachycephaly, on the one hand, or dolichoceph­aly on the other, as shown in the accompanying cut. The rudimentary horns, at first barely no­ticeable as the faintest convexities of the skull invariably appearing at the junction of the frontals and nasals, and produced by a thicken­ing of the cellular spaces, are first observed of equal size in the males and females; later they become more prominent in the males than in the females; finally they assume vast proportions in the males and present an arrested development in the females. At the summit of the Eocene the extreme dolichocephalic and brachycephalic phyla die out, and in the Oligocene a new series of phyla arise. Among these the long-horned forms appear through selection to develop the horns at the expense of other characters, the males ,vith the longest horns probably securing the most females and becoming the chief breed-

248 DARWIN AND P ALEONTOLOGY

ers. It is especially note,vorthy that in these long-horned phyla the main incidence of selection seems to be diverted to the horns from the teeth ,vhich appear to be d,varfed or arrested in evolu­tion. In the short-hol'ned phyla, on the other hand, including one Sel'ies at least, protected by more slender limbs and more rapid movements, the teeth are constantly sharpened and improved; this may be interpreted as caused by the selection of changes of proportion in the teeth.

The teeth, however, of all these phyla of titanotheres are of a mechanical type ,vhich does not admit of further evolution; they have reached a stage 1,vhich is a cul-de-sac,1 beyond ,vhich no progress is possible. The change of environment and of flora, therefore, finds these animals inca­pable of further mechanical betterment either through heredity or through the selection of vari­ations of proportion. All the titanotheres be­come suddenly extinct, and it is note\vorthy that all other herbivorous quadrupeds having this cul­de-sac type of grinding tooth also became extinct in North An1erica and in Europe either during the Oligocene or J\1iocene periods.

'l'his is an outline of the only theoretical inter­pretation which can be offered at present. In it heredity, ontogeny, environment, and selection are supposed to be in continuous interaction or

' Osborn, H. F.: "Rise of the Mammalia in North America." Vice-Presidential Address before the American Association for the Advancement of Science. Section of Zoology. Madison, Wis., August 7, 1893.

DARWIN AND P ALEONTOLOGY 249

interplay. One feature has been omitted: that is, that all the branches of all the phyla, ,vith one exception, sho,v a continuous and progressive in­crease in size. This increase in size is, ho,vever, itself interpreted not only as a response to f avor­able environ1nent, but also to the selection of he­reditary variations in size due to the fact that the larger quadrupeds are better able to stand off the attacks of their carnivorous enemies.

CONCLUSION

This interpretation, finally, is seen to include the cooperation of factors recognized by Buffon, by L amarck, and by D ar,vin, except as to the transnussion of acquired characters, ·which is left in doubt. There is, ho,vever, a ne,v principle in the " mutation of '\Vaagen " or " rectigradations of Osborn," unkno"'n to Dar,vin and due to causes entirely unkno,vn to us at the present time, and perhaps, as already intimated, unkno,vable. In this connection it is interesting to recall the comment of Aristotle 1 on the survival-of-the­.fittest theory (the bracketed insertions [ ] and itallics are our own):-

" What, then, hinders but that the parts in Nature may also thus arise [namely, according to law]. For instance, that the teeth should arise from necessity, the front teeth sharp and adapted to divide food, the grinders broad and adapted to breaking the food into pieces.

• Osborn, H. F.: From the Greeks to Danoin, Svo, I\IacmiUan & Co., 1894, p. 55.

~50 DARWI N AND PALEONTOLOGY

" [ Another explanation may be offered.] Yet, it may be said, that they were not made for this purpose [i.e. for this adaptation], but that this [adaptive] purposive arrangement came about by chance; and the same reasoning is applied to other parts of the body in which existence for some purpose is apparent. And, it is argued, that where all things happened as if they were made for some purpose, being aptly [ adaptively] united by chance, these were preserved, but such as were not aptly [adaptively] made, these were lost and still p_erish, according to what Empedocles says concerning the bull species with human heads. This, therefore, and sim­ilar reasoning, may lead some to doubt on this subject.

" It is, however, impossible that these [adaptive] parts should subsist [arise] in this manner; for these parts, and everything which is produced in Nature, are either always, or, for the most part, thus [i. e., adapt­ively] produced; and this is not the case with anything which is produced by fortune or chance, even as it does not appear to be fortune or chance that it frequently rains in winter. . . . I f these things appear to be either by chance, or to be for some purpose, and we have shown that they can not be by chance, then it follows that they must be for some purpose. There is, therefore, a purpose in things which are produced by, and exist from, Nature."

Paleontology at present seems to support the philosophical contention of Aristotle, that ·when ,ve come to the minute slo"rly progressing in­ternal changes, the fittest originates in la,v.

EVOLUTION AND PSYCH OL OGY

BY

G. STANLEY HALL

DAR,VIN'S CONTRIBUTION TO PSYCHOLOGY

T HE contributions of D ar,vin to psychology, h.ave not been adequately recognized. Not only in his famous seventh chapter on " I nstinct" in the Origin of Species; in the second and third in the Descent of 'IJI an, comparing the psychic po·w­ers of men and animals; in his Expressions of E 1notions, and in Doniestication, but sometimes in other works, he not only showed a depth of in­sight into, but laid anew the foundations of, genetic as ,vell as comparative psychology. T hese should, and I believe will, eventually make him regarded as hardly less the founder of a ne,v departure in this field than in that of classifica­tion, form, and structure. F or him the soul of man is no ,vhit less the offspring of that of ani­mals than is his body. Our psychic po,vers are ne,v dispensations of theirs. The ascending series of gradations is no more broken for the psyche than for the soma. T he. gaps aTe no wider or more numerous from the lo,vest t o the highest in the one than in the other. The affini­ties and analogies are as close, and the soul in-

251

~5~ EVOLUTION AND PSYCHOLOGY

herits as much from our venerable, brute for­bears as does the body. The rudiments are as numerous and, to those who can rightly interpret them, as significant. From the higher anthro­poids, we need to go down the evolutionary stage but a little ·way to span an interval quite as great as that separating even the existing great apes from the lo,vest savages.

But Darwin's method is always and every­where objective and observational, never sub­jective or introspective. Fe,v who have ever ,vritten about the mind of man kno,v or say so little about consciousness, ,vhich has spun its l\1erlin spell of enchantment about our craft and all its ,vo1·ks and ways. His language is the con­crete facts of life and mind, and not the categories and intuitions that an ingro·wing intellect loves to manipulate. The brute soul explains that of man, rather more than man explains the brute; the unconscious explains the conscious and not conversely. He posits: a natural history rather than a philosophy of mind. As Steinthal said language could be studied only historically­" Sie ist ,vas sie geworden "- so for Darwin the true, ultimate knowledge of our psyche is the de­scription of all developmental stages fron1 the amooba up; and those move most surely a1nong the altitudes who have most carefully explored the depths in ,vhich the highest human po,vers originate. Emotions are best studied in their out,vard expressions in gesture, ,vill is investi-

EVOLUTION AND PSYCHOLOGY !253

gated by the study of behavior, intelligence by massed instances of sagacity, and not by analysis under old rubrics. While .he would have wel­comed all the illuminating experiments and tests under controlled conditions, ,vhich have lately given us such a wealth of insight, he ,vould prob­ably have pref erred careful observations of ani­mals afield in their accustomed habitat. Let us psychologists find in this celebration motivation to re-read his masterful contributions to our sci­ence, for nothing in our perhaps all too copious literature so gro,vs upon the mind by frequent 1·eperusal; and thus only shall we profit to the full, as ,ve have been tardier than the biologists in doing, by the method, direction, and inspira­tion he so abundantly offers us.

GENETIC SYNTHESIS THE NEED OF l\.fODERN PSYCHOLOGY

Probably most psychologists in our day accept evolution in a general way and have only praise for Dar,vin; yet I can think of but very fe,v whose interest in the studies of the soul is pre­dominately evolutionary or very much influenced even by Herbert Spencer. Students of instinct have profited most here, although many of theii­studies are made under a1-tificial and highly­specialized aspects, ,vith too little reference to life history and habits of the species in the state of nature. The human mind is, for the most part, no,v studied introspectively, not only by the

~54 EVOLUTION AND PSYCHOLOGY

literary psychologists but in the laboratory, ,vhich is more and more regarded as a method and microscope of subjective analysis. Even Wundt approached psychology from the stand­point of physics and physiology, and his great text-book ,vould have been but very little differ­ent had Dar,vin never lived. The doctrine of apperception and even of feeling, ,vith its recent, labored, introspective discussions of peripheral versus central origin and tri-dimensional theories, very rarely considers any developmental aspects; and this is one reason ,vhy, as has lately been so ably pointed out, neither Wundt nor the other standard text-books offer any aid to the student of abnormal psychology or of instinct.

Mean,vhile, our science has had a prodigious and sudden horizontal expansion far beyond the old themes and limits. v\Te have a psychology of religion, ,vith a 1nore special literature on such subjects as conversion. atonement, faith, posses­sion, holy spirit, inspiration, imn1ortality, proph­ecy, prayer, Sabbath, and even the process of dying, sin, and demonology. Then there is the new psychology of crime, under its special ru­brics, murder, theft, arson, rape, suicide, fraud, and swindling, ,vith traits of the chief classes of criminals. Hypnotism and suggestion, not to mention ghosts and telepathy, have opened an­other field. Then ,ve have the psychology of sex in its normal and morbid manifestations, psychic differences, eugenics, and moral prophy-

EVOLUTION AND PSYCHOLOGY ~55

laxis. There is the psychology of language, ges­ture, n1usic, unitation, social instincts, truthful­ness, infancy, childhood, adolescence, pedagogy, property, play, genius, and prodigies, sleight-of­hand, advertising, ,var, second breath, leader­ship, provincialism, business and panic, psy­chic epidemics, and 1nany more, not to speak of the long list of admirable studies of excep­tional individuals from I-Ielen l(eller to Miss Beauchamp, Flournoy's l\1lle. Smith, Beers, Monod, and Mrs. Piper. Instead of restricting himself to the classic, old themes of 1nemo1·y, as­sociation, logic, freedom of the will, conscience, in more or less academic seclusion and aloofness, the n1odern psychologist is often consulted by parents, pedagogues, lavvyers, legislative corn­Inittees; lectures before popular audiences; or writes books and articles in a catchy, impression­istic style, ·with great attention to phrase-making.

T hus, present themes are so absorbing, so n1any and so ne,v, that if ,ve are not beginning to lose sight of each other, ·we have lacked time and incentive to keep posted and interested all over the field, until no,v the task has gro,vn beyond the ability of any one less gifted than D arwin to mas­ter details, see perspective, and mosaic items into true, evolutionary order ·which can alone bring unity into this teeming but now chaotic domain. The material for perhaps the most majestic struc­ture yet reared by science is already quarried. The need of and call for a master builder in this

~56 EVOLUTION AND PSYCHOLOGY

neld must, ere long, produce the man. Some of us are already convinced that the human soul in all its power is just as much a product of evolu­tion as the body; but our faith needs to add the kno,vledge that can only come when all the au­thentic data are properly grouped_ That the impending synthesis must be genetic, not in the prolix and platitudinous sense of Spencer, but ,vith concrete facts as warp and ,voof, is inevita­ble if the psychology of the future is to correlate the facts of instinct, of daily human life with all its hot and intense impulses and all its morbid manifestations, and so become the :Bible of the soul of man, in a sense our cun·ent, fragmentary systems do not dream of-this seems to 1ne to be self-evident.

RUDIMENITARY PSYCHOSES

The signs and f oregleams of such a recon­struction and transvolution are already many. In abnormal psychology, devolution is a rubric of increasing dominance. The J aclksonian the­ory of epilepsy brings in the genetic perspective in its conceptions of higher and lo,ver levels. The studies of sex perversions are replete "';th references to the past history of the race, and some of them can be explained only as reversions, as in the case of the impulsions to nudity and ex­hibitionisn1. 1'1any of the psychic facts in hu­man courtship point directly to that of animals. Some of the laws of the long-circuiting of the

EVOLUTION AND :PSYCHOLOGY 257

genesic instinct into secondary sex qualities are the same for brute and man. The more ,ve kno,v of this instinct the more orderly and unbroken becomes the progression upward and the closer the parallel. Even the differences are more and more explicable. The same is true of the care of the young, where the basal phenomena are common to all the higher mammals, and some of then1 to all viviparous creatures. Again, the cor­respondences bet,veen adolescence and senescence are, in some cardinal points, strangely comple­mentary. Here, too, should be mentioned the striking morphological, pathological, and psychic indications f ron1 the study of childhood that puberty once came much earlier in our for bears, the auto genetic inferences in this direction, how­ever, being as yet too slightly supported by phy­letic facts, on account of the necessary imperfec­tions of the record. Perhaps best of all as an il­lustration is the new psychology of crime and cri1ninals, ,vho are so shot through, body and soul, ,vith atavisms that only the early history of the race can explain them.

Again, if ,ve eliminate from the later studies of n1ental diseases, all the evolutionary elements and suggestions, they ,vould be robbed of no lit­tle value. I ref er especially to psychasthenic and dissolutive states, to certain of the phobias, fuges, imperative ideas, to various eruptive or fulminat­ing phenomena and psycholeptic crises, and to the formation of the more or less subconscious con-

~58 EVOLUTION AND PSYCHOLOGY

stellations of psychic elements, ·which may act like foreign bodies in the soul, and some of ·which are peculiarly suggestive of atavistic or outgro-wn states. Here, too, belong many phenomena of hypnoidization ·with more or less psychic decapi­tation-Verdichtung- ( ,vh.i.ch probably repre­sents a type of psychoses that are peculiarly characteristic of prehistoric man, who ejected his subjective states much as Freud thinks that dreamers are doing, to say nothing of the latest studies of phonisms, photis111s, and coenesthesias. It is studies in this field, it may also be men­tioned, that have led acute minds, like Bleuler, to violent polemics against consciousness as the muse of modern psychology, some of them insist­ing that but little of the experience that has made the mind in its human form has been connected with either consciousness, apperception, or even attention. 1'he vie'"v is unquestionably gaining ground that consciousness is an epipheno1nenon of mind, and that its function is essentially no less remedial or cathartic than the church has held confession to be, though in a some·what dif­ferent ·way. There is no better test of a psycho­logical system than its applicability to psychi­atry; and it is here that ,vundt so signally fails, for his fundamental asswnption is that conscious­ness is the condition of all psychic experience, and he defines even feeling as a" subjective reac­tion of consciousness." In fact, on the contrary, there are incessant and man.if old affective and

EVOLUTION AND PSYCHOLOGY ~59

other processes going on in us that lack conscious­ness, although they often resemble it in them­selves and in their influence upon us, and which can not be ignored because they of ten dominate psychopathic sympto1ns and also our normal lives. These are processes ,vhich become con­scious only ·when associated with the ego-com­plex. l\iany sudden choices, movements, feelings of anger and fear, and many other experiences sometin1es lack all intellectual motivation as much as do melodic haunts. I t is such states and activities, possibly 1nediated by sub-cortical areas, that irresistibly suggest past evolutionary stages of mentation, and it is also this group of under­lying processes that may put on and off suc­cessive, conscious personalities as garments. It is these deep yet dominant complexes that love, hate, shape many currents of conduct, before con­sciousness is aware of it, and which are constantly reinforcing and approving or censuring what con­sciousness does. They suffer or rejoice sometimes with, sometimes without, consciousness, which is only their very imperfect instrument. Per­haps nothing is ever fully conscious, ,vhile much that takes place in us may be wholly unconscious. T o say with Raimann that " there is no uncon­scious knowledge"; or with H ellpach that "psy­chology deals only with consciousness," and that "the unconscious can not be an object of kno,vl­edge," is a form of psycho-physic parallelism that amounts to obscurantism; ,vhile to urge, as ,ve

~60 EVOLUTION A'ND PSYCHOLOGY

must, that even attention may be unconscious ,vould shock even an alienist so speculative as Ziehen, who persistently identifies the psychic ·with the conscious.

PSYCIC " RECAPITULATION"

Hardly less than ani1nal instinct, child psy­chology, as D ar,vin in his famous observations on infancy, although not the first was perhaps the third to see, can only be explained on an evolu­tionary basis. T he child, uncivilized and to some extent even savage, is precociously thrust into an environment saturated ,vith adult influences because of language and accun1ulated gro,vn-up customs, traditions, and ideas; and for this rea­son as well as because of its intense, imitative pro­pensities tends to be very early.stripped of many of its psychic rudiments and recapitulatory traces. Yet the more ,ve kno,v the child, the more clearly do we see the germs of many ata­vistic tendencies nipped in the bud, though many of them have so long been. There can no longer be any doubt that the hun1an infant not only tends to but occasionally does develop real ·words that are its o,vn original creation, products of the rudiment of the san1e instinct in ,vhich language took its ifirst rise. This vestige is thus not com­pletely eliminated by the early, mi1netic adoption of the speech of the environment. I have col­lected from the literature over t,vo score of these

EVOLUTION AND PSYCHOLOGY ~61

,vords ,vhich, I believe, can not possibly be ex­plained as imitations, and ,vhich have been used consistently by the child for some time and occa­sionally for a number of years. So in infantile dra,ving ,ve have undoubted, though dwindlling, traces of ,vhat Verworn calls the physioplastic stage of paleolithic man, before the idioplastic stage of the neolith, ,vho ceased to draw directly from the object itself but rather copied his o-wn mental iinage of it. Here, again, a well-recog­nized phyletic stage has d,vindled to little more than a filmy vestige in the n1odern infant, but is as recognizable as the rudimentary gill-slits in the embryo. The swimming, paddling move­ments, too, by new-born infants if _supported in tepid ,vater; the \Vonderful po·wer to cling and support the ,veight for a minute or t1-vo during the first few \veeks after birth, a po\ver soon lost but reminscent of arboreal life; the phobias of infants of a few ,veeks or months seen often in nervous shudders at the first i1npressions of fur, big teeth and eyes; the joy experienced by toss­ing and other levitation movements, creeping, and the processes of assuming the erect position; the very intricate and interesting stages of the progressive acquirement of the complex sense of self; the loud cry of the human infant from birth on as contrasted with the silence of the new-born of other ani1nals, so eloquent of the early pow·er of the parent to protect; and for older children fetishisms galore, gangs corresponding to the

262 EVOLUTION AND PSYCHOLOGY

primitive tribes, propensity for hunting, killing, striking with clubs, pounding, stealing, etc., the sense of the po"ver of the point, edge, string, and many forms of plays and toys, the nascent sense of death, and other items far too numerous to even catalogue here- all sho,v that the child is vastly more ancient than the man, and that adult­hood is comparatively a novel structure built upon very antique foundations. The child is not so much the father of the man as his very venerable and, in his early stages, half-anthropoid ancestor. T here can no longer be any question that its rudimentary psychic organs are no whit less numerous than the half-score of anatomical rudiments that Wiedersheim enumerates. Per­haps, in general, the traces of the psychic reca­pitulation of the history of the race are most traceable and most unbroken, faint as some of the traces are. Psycho-genesis, like embryology, sho,vs many rudiments preserved and developed by being diverted to other than their original uses, although of very few psychic traits or func­tions have there been adequate material methods of record and preservation as structural details are preserved; nevertheless, they follow the same lapidary law and speak a language ,vhich, when it is set down and interpreted, is no less clear and certain.

I n general, nearly every act, sensation, feel­ing, will, and thought of the young child tends to be paleopsychic just in proportion as the child

EVOLUTION AND PSYCHOLOGY 263

1s let alone 01· isolated fron1 the influence of gro,vn-ups, ,vhose presence al,vays tends to the elimination of these archaic elements, and in all cases n1akes havoc ,vith them, over-repressing some that should have their brief fling, if only on the principle of the Aristotelian catharsis, to give early immunity fron1 the hypertrophy of bestial traits by a,vakening the next highe1· pow­ers that repress them in their nascent period; but '\vhich, in some environments, are left to grow into faults and then into juvenile crimes, which they are prone to do just in proportion as the order of their nascency is perverted. Thus the p1·oblem of a true mentally, esthetically and morally or­thopedic education still gropes in the trial and error stage, although not ,vithout some progress toward a scientific basis for pedagogy ,vbich, if i t ever comes, can rest on no other foundation than a well-established embryology of the soul, :all the ·way from eugenics and the psychic states .and regimen of pregnancy on to the f uUy ma­tured nubility of the offspring. Thus, from one point of vie,v, infancy, childhood, and youth are three bunches of keys to unlock the past history ,of the race. Many of the keys, especially those which belong to the oldest bunch, are lost and others are in a11 stages of rust and decay. l\1any of the phyletic locks ·which they fit are also lost or broken; both locks and keys are of ten dis­torted and, to change the figure, the sequences which the race f ollo,ved are often inverted in the

~64 EVOLUTION AND PSYCHOLOGY

autogenetic proce~~ional of growth; but, if the goal is still dim and far, it is unmistakable, and as we slowly and surely approach it, the genetic psychologist feels it beckoning, calling, and in­spiring, almost like a new muse. Tlhis has intro­duced a temporal perspective or ne,v dimension into a field where most preceding and even pres­ent studies have all been in the flat surface of the present state of adult consciousness. This is sup­ported by, though still but very imperfectly cor­related with, the studies of animal instinct on the one hand, and with those of the myth, custom, and belief of primitive races on the other. It already suggests to the many laboratory studies of the affective life (based on the method of controlling the conditions of very slight variations of emo­tional tone exigously made and based only on a f e,v adult experts), a more excellent way, which ,vould t~d to bring psychology back to the study of human life as it is lived out, ,vhere it is hottest, most intense a.nd passional ,vith love, anger, fear, hate, jealousy, grim and dour struggles with sin, wrought out ,vith sweat, blood, and supreme effort, with perhaps the life and death of the indi­vidual or even the race at stake. Here, rather than in the isolation of the laboratory or the study, lies the heart of a psychology that touches life and that really avails and has ,vorth and value, because it is in line with the eternal pow­ers and is, in a word, a true, natural history of the soul, and can make " philosophy " again, as

EVOLUTION AND PSYCHOLOGY ~65

the motto of one of our best-known culture fra­ternities has it, " the guide of life."

THE PSYCHOLOGY OF THE FUTURE

Finally, education, no,v perhaps the most uni­versal and uniform of all the social institutions, is no,v looking to psychology for guidance as never before, and ,ve are at present able to meet this call in only a halting and partial way. Re­ligion seems of late to be beco1ning strangely docile to all the too little we have to teach it. Psychiatry, to "'hich we should have at least given a science of normal psychic life, is now in danger of finding our texts of little avail in solv­ing its problen1s, is building ne,v foundations of its o,vn, and gro,ving weary of our sophistic sub­tleties concerning parallelism and interaction and the nature of feeling, conscience, etc. Few, even of our recent experimental results, are available for determining or influencing normality or aL­no1mality; our discussions of freedom, necessity, or responsibility are too academic for use in crim­inology. The great ne,vly discovered continent of the unconscious is still regarded by many 1nem­bers of our guild as mystical, perhaps superlj1n­inal, and its phenomena are used to cast augu­ries as to ,vhether the soul is independent of or survives the body. The unconscious is really like the submerged eight-ninths of an iceberg, which is impelled by deeper currents in a denser medium, and which the glittering sumlnits that

~66 EVOLUTION AND PSYCHOLOGY

emerge above the tide and are impelled by only atmospheric pressure have little control over. And once more, just as psychiatry is now chang­ing its emphasis from a predominantly somatic and neurological basis, which has been so fruitful under the old slogan of Virchow, " Ubi est mor­bus," to a more psychic, pathological vie·wpoint, so perhaps even the doctrine of heredity is com­ing our way by changing the terms applied to its elements from the mystic, pathological ids and dete1·minations of Weismann to Semon's no less mystic but psychological postulates of mnemes and engrams. Here, too, vve are hardly ready to meet the new demands or utilize the new princi­ples, because our department is still, despite its great, recent progress, only half scientific and is not unlike lV[ilton's ne,v-born ta,vny lion pa,ving to get away from the metaphysical and theolog­ical soil from which it sprang. ,v e have too long yielded to the seductions of the heterai of the ancient, speculative problems that have ob­sessed us and not yet definitely broken ·with those in our midst who still urge that psychology should be developed in the closest rapport with, if not under the influence of, a speculative phi­losophy.

Finally, as Darwin freed biology from the in­veterate dominance of the ideas of fixed and divinely created species, conceptions directly in­herited from Plato's ideas and Aristotle's cate­gories, so everything in the present psychological

EVOLUTION AND PSYCHOLOGY ~67

situation cries out for a ne,v Dar,vin of the mind, \vho shall break the persistent spell of theoTetical problems incapable of scientific solution, the ideal of a logical and methodical exactness greater than our subject in its present stage pern'lits of, 'ltvh.ich Aristotle ,vell dubbed pedantry, and re­n1and the haunting proble1n of the ultimate nature of consciousness and the final goal of the psyche to the same limbo, by suspending convic­tions, as those of the constitution or cause of energy and the nature of reality and objectivity. Only by so doing can ,ve again get up against the essential facts of life as it is lived out by the toil­ing, struggling men, women, and children, nor­n1al and defective, of our day. If this rough diagnosis of the present situation is correct, only a pessi1nist can doubt that the need will, ere long, bring the man or the n1en to meet it in the only ,,·ay it can be met, viz., by a comprehensive evo­lutionary synthesis in the psychological don1ain, '"hich by every token seems at present to impend.

INDEX

Acquired character.s, inheritance of, 34-43, 111, ll!il, 1'20-1'24-, 197, 204-206

Adaptation, 41, 61-66, !llS; ab­sence of, 61-66, 85; in muta­tions, 178; address on, 182-208; functional, '20S

Adapted environments, 189, 186 Adapted faunas, 184 Adjustment, self-, 42; to en-

·vironment, 116 AoAssIZ, Alexander, theory of

coral islands, 9 Ao1.ss1z, Louis, unfavorable to

Darwin, 27 Albinism, 155, 169 ARGYLL, Duke of, views of, 45 ARISTOTLE, quoted, !349 ARRHENlUS, on origin of mat-

ter, 46 A-rtiftcial selection, 7 4; isolation

in, 85 Aster, evolution of genus, SS, 59 A then<I!um, review of Origin in,

20

B.AILEY, on pouched gophers, 76 BALDWIN, J. M., organic selec­

tion, 10, 48; effect of social environment, SO

Barriers in species formation, 81, 84

BATES, H. W., hypothesis of mimicry, 47

BATESON, W., variation in Kal­lima, 178; variation, 224-227

Beog/6, voyage of the, 8, 11, 12, 192, 215

BECCAllt, theory of evolution, 24, :JS

Beetles, experiments upon, 124 BENTHAM, 19 Blind fishe8, 189, 190, 200 B LOMEFIELD, L., word " muta­

tion," 4S

BONNET, C., forerunner of pan­genesis, 95

Botany, debt to Danvin, 51 BovzRI, T., chromosome theory,

IOS, 104 Brachiopoda, 210, 211 BaA1Nz11.o, E., violets, 166 BaowN, R., 18 Bud-sports, ISO BurroN, SI, 215, 249; adapta­

tion, 193, '204; evolution, 20; pan genesis, 95

BU11.cHELt., W. J., 19; feelings in forest, 58; isolation, 90

CARLYLE, Mrs., on Owen, SI CAil.Pi: NTEa, 19 CASTLE, W. E., address by, 143-

159 Catfishes, '200 Cathedrals as awe inspirers, S6,

37 Cave faunas, 184, 186-190 CelJ, in heredity and evolution,

92-113 CaAMBERLU<, T. C., address by,

1-7 CHAMBERS, R., evolution doc­

trine, 20 Characters, acquired (see: Ac­

quired characters); new, 68-61, 22S-23S; origin of, 58-61; unit (see: Unit character)

Characins, 192-196, '20S Chemical nature of heredity,

107, 163, 180 Chromatin, 99-104 Chromosomes, in fertilization,

100, 103; radium on, 129, 138; rale of, 101

Climbing plants, debt to Asa Gray, 29

Cognate species, 81 Coleoptera, experiments with, 12 Color, men deli an phenomena in,

108, 152, 169

•

~70 INDEX

Combs of cocks, Hl7, 171 Contiiu,ity of germ-plasm, SS Continuous evolution, 48-50 CoP£, E. D., 9, !115, 229, 232 Coral islands, Darwin's theory

of, 46 Coniu:Ns, C., rediscoverer of

l\fondelism, 145 Cour.s, E ., quoted, 78 CouLTER, J. M., address by, 57-

71 Crime and evolution, 256 CRocJ<ta, \V., work on seeds, 62 CU\rJ£R, G., flS Cytoplasm i n hered ity, 101

DANA, theory of coral islands, 9 DAnW1.N', C., 249; influence, I;

early life, 11; first attention to evolution, 7; first sketch of O,·igin, IS; prepares for pub­lication, 18; maturity of the Oi-igin, !'13; thrilled by anthem, SS; on Leicester sheep, 76; on isolation, 87; on mutation, 43-45, 163-165; work on galls, 131, 132; on black peacock, 169; adaptation, 193; rela­tion to paleontology, 212; psychology, 251-254, 260 ; let­ters: Hui<ley, 10; Owen, 31; \V right, 32; Leidy, 209 ; Davidson, 910

DARWIN, Erasmus, Zoo11omia, 10; evolution, 20

DAnW1N", Francis, on acquired characters, 39; p residelltial address, 39; letter about galls., 132

DAVENPORT, C. B., address by, 160-181

DAvwsoN, L., letter from Dar­win, !HO

Definite variations, 931 DE VRIES, H., !Uf.l; intercellu­

lar pangenesis, 93, 106, 144; premutation period, 132; re­discoverer of .Mendelism, 145; mutation theory, 160, 2;19; cessation of selection, 174; adaptation, 193

Differentiation and cytology, 105

Directed variation, 236

Discontinuous 140, 180, 2-27,

Douo, L., 229

evolution, 228

48,

Ecology, 61 Edinburgl, Rettie10, article by

Owen, 31 Education and e,,olution, 2G3,

265 Effect of Origin, 64, 55 E1c,:N>1ANN, C. H., address,

182-208 Et>IER, T., orthogenesis, 193 Elementary species, 166 Elimination, 176, 177 Emotions and evolution, 251 Entclechy, 110 Environment, adjustment to,

117; factor in evolution, 244 Enzymes in heredity 106-109 Evening primrose, 130, 133, 165-

166 E'°olt,tion first brought to Dar­

win's attention, 8; of Gymno­sperms, 66-70; isolation in, 72-91.; cell in relation to, 92-ll3; role of envi ronment in, 114-142; and psychology, 251-266

Experimental rnorphology, 61 Extra-floral nectaries, 63 External factors, 115, 126, 197-

207, 938, 2$9

Factors of evolution, 23S Factor hypothesis in heredity,

108, 115, 150<-158 FARRER, Lord, letter of Dar­

win to, f.!5 FAWCETT, H., defcnse of Dar­

win, 8; letter to, from Dar­win, 21, 2:?; review of Origin, 2:i, 34

Ferments in heredity, 106 Fertilization of egg, 10S F ,scnEn, E., experiments, 1:13 F1sK£, J., evolutionary teaching,

9 FITTON', 19 Fluctuation, limit to, 49, 173-

176; in isolation, 85, 173 FonnEs, E., coral reefs, 46;

views on arctic relics antici­pated by Darwin, 46

INDEX. ~71

FoRD£S, s. A., quoted, 167 Forests, excite feeling, 96 Forms of Flower.a, dedicated

to Asa Gray, !i!9 Fortuitous variation, 226 Freshwater fishes, 18,t. Fnnro, 258

GAGE, S. H. and S. P., experi­ments, J:ll

GAGER, C. S., experiments with radium, 1:18, 138

GAuLEo, effect of teaching, 55 Galls, vegetable, 131 GALTON, F., effect of Origin,

Ml; experiments on pangen­esis, 145

GXnTNEB, hybridization, 55?, 53 GAUDRY, 215 Geminate species, SI Gemmules, 95, 96 "Genesis of Species," S!l Genetic synthesis in psycholo$Y,

253 Geographic conve~gence, 199,

201; distribution, 73; varia­tion, 181, 196-198

Geologic convergence, 200, 201 Germ-plasm, continuity of, 35,

40; influence of soma. on, 120 Goats, 164 Gooseberry, cessation of varia-

tion, 176 Goss£, P ., Omphalos, 15, 16 Graduated ~hnracters, 127 GRAY, A., clcfense of Darwin,

8; friendship with Darwin, 26-29; Darwin's opinion of, 26; correspondence with Dar­win, SI, 44

GREGORY, W. K., 243 GROVE, Dr., intenriews Tenny ...

son, 15 Guinea-pig, 148, 14-9 Gu1.1CK, J. T., 193 GURNEY, E., letter of Darwin

to, 35 GoTHRr£, C. C., experiments,

205 Gymnosperms, phylogeny, 60;

evolution without utility, 66

HAECKEL, E., on pangenesis, 40 Hair, 151, 170

HA 1,L, G. STANLEY, address by, f.!51-267

HALL, JAMES, the fossil record, 9 HAt,LE'IT, cessation of improve-

ment in wheat, 48 HELLPACH, 259 HE NFREY, 19 HENSLow, J. S., friendship with

Darwin, lJ ; opinion of Lyell's Geology, 12; Jetter of Darwin to, 96

HeTedity (sec also Inheritance), c"liemical nature of, 110; and memory, 112; determination of, 114; unit characters in, 143-159; of mutations, 171; factor of evolution, f.!44

HE1t1No, on heredity, 39 HEnTwm, O., the nucleus in

heredity, 99 HtwENDORF, work of, 214 IioF>r£1s~1rn, on plant relation­

ships, 57 HooKEn, Sir ,Tos<Pll, clefense of

Darwin, 8; advice asked by Darwin, 18; presents papers of Darwin and 'Wallace, 18, 19; utility, 25; friendship with Darwin, 25, 26; letter of Dar­win to, about Mivart, Sf.!; about pangenesis, 39; about limits to artificial selection, 48; coral reefs, 46; letters from Danvin, 51, 94, 131

Ho,oKER, Sir W tLLLut, letter from Burchell to, 3S

Hormones, 106, 109, 112 Horns, 147, 164, 170, 240, 247 HonN£R, L., letter to, 12 Horse, 175 HoirnouYr, Darwin on, S6 HuxLEY, T. H ., 215, f.!i.14; letter

of Darwin to, 10; friendship with Darwin, 29; reviews Origin, :33; effect on study of biolo$Y, 53; on coming of age of the Origi?t, 54; op­posed to pangencsis, 93

HYATT, A., controversy with Darwin, 9; the fossil record, 9; work of, 212, 213, 231

Hybridity, and selection, 52; characters swamped by, 141, 179

INDEX

Idioplasm, 99 Inheritance of acquired char­

acters ( see Acquired char­acters)

Intelligence and evolution, !/SS Intercrossing, checked by isola-

tion, 75 Internal secretions, 109, 119 Intercellular pangenesis, 93 Island faunas, 81 Isolation in evolution, 751-91;

rule of, 75-80; and differenti­ation, 198

JAMES, "'·• leader of American psychology, 10; quoted, !124

JoRDAN, DAvto STABB, address by, 71-91

Kallima, 177 Karyokinetic division and he-

redity, 103, 104 KINGSLEY, C., quoted, 16 KoLREUTER, hybridism, 551 KOWAl,EVSKY, 5100, !115

LAMARCK, Erasmus pothesis, 193, 5104

215, !149; debt to Darwin, 10; hy-

34, 35; adaptation,

LANE-CLAYPOLE, effect of fetus extract, 107

LAN KESTER, E. RAY, quoted, 99; "homoplasy," 5140

Leaf-butterfly·, 177 LEIDY, J., S/351; fossil record, 9;

correspondence with Darwin, 909

Lepidoptera, experiments upon, 1513

Linnean Society, meeting for Natural Selection papers, 18

Li.zards, 200 LOTSY, J, P., 166 LYELL, CHARLES, influence on

Darwin, 12, 13, 29; presents the papers of Darwin and Wallace, l 8, 19; prevents Dawson's review, 21; letter of Darwin to, 45; coral reefs, 46

MAcDouoAL, D. T., chemical treatment of germ-cells, 110; address by, lH,

MAcGREcon, expel'iments, 128 MALTRUS, influence on Darwin,

11 Mammals, fossil, 21S Mammary glands, stimulated by

fetus extract, 107 MARSH, 0. C., 9, 215, 918, 239 MATTHEWS, 213 Maturation, 103 May beetles, 167 Memory in heredity, 41, 112 MENDEL, G., 145 Mendelism, 10, 144, 242; and

pangenesis, 40; and here,lity, 100, 108, 152, 153

Metabolic actfrities, irritable re­actions, 117

MILL, J. S., opinion of Origin, 29, 23

:Mitotic division in heredity, 102

l\:hvART, ST. GEonoE, opposition to Darwin, 81-33

111ooRE, AUBREY, quoted, 17 MORGAN, LLovo, organic selec­

tion, 10, 48 MOLLER, Fa1TZ, defense of Dar­

win, 8; letter of Darwin to, 39 MuRRAY, ANDREW', crude theory

of, !14 Mutation, 202; bearing on pan­

genesis, 40; Darwin's views on, 43-46; origin, Ill; ad­dress on, 160-181; and adap• tation, 194

Myrmecophiles, 63

N .&CELI, theory of evolution, 25; idioplasm, 144, 146; adapta­tion, 193

Natural selection, 206; theory of, 10; discovery of, 11; pecu­liarities of, 14; opponents of, 24; claimed by Owen, 31 ; in relation to m .. tation, 47; to hybridism, 52; to botany, 57-71 ; implies segregation, 85; not opposed to isolation theory, 89; and mutation, 176; and adaptation, 19l?, 196

Neo-Darwinism, 161-163

INDEX !t73

Neo-Lamarckism and paleontol-ogy, 9, !?37

NEUMAYER, !!13, 231 NEWTON, effect of teachings, 55 Nucleus, in heredity, 99, 105,

106 NUSSBAUM, M:., 98

o'OamoNY, A., 12 Ou,•u, 19 Ontogeny, factor of evoluUon,

241 Organic selecUoo, 10, 48, !!37 Origin of life, not a subject

for speculation, 46 Origin of Species, recepUon of,

!l, 20-23; influence, 6; attacks on, 51

Orthogenesis, 111, 197, !?34-240 ORTMANN, quoted, 77 OSBORN, H. F., 11. !i!lS, !i!Sl;

fossil record, 9; theory of organic selection, 10, 48; or­thogenesis, 193; address by1 >109-250

OwEN, R., Sl; evolution doc­trine, 20; attack on Darwin­ism, SO; characters of fossils, 232

Oxroao, bishop of, attacks on Darwinism, 30

Oxford University, IS, SS

Paleonlology, adclre.ss, 209,250 Pangeoesis, 35, 39, 40, 92-97,

106, 144, 236 Parallel adaptations, 80 Peacock, black-shouldered, 169 Peas, 146 Pedagogy and evolution, 146 Penstemon, 135 Permanence of ocean basins, 46 Philo8ophie zoologique of La-

marck, 11 PtCTET, nutrition of egg, 121 Pigment, 147 PolyphyleUc origins:, hypothesis

of, 9 PouLTON, E. B., 236; address

by, 8-56; Darwin's views on variation, 217

Poultry, 168-174 Psychical nature of develop­

ment, 109

Psychiatry, 265 Psychology and evolution, 251 Pterydopbytes, 70

Rabbit. 149-159 RAJJL, c., 103 Radium, effect on germ-plasm,

1!!7-130 RAIMANN, 259 Recapitulation in psychology,

260 Rectigradation, >131, 2:34, 239,

242 Regeneration, Darwin on, 99, 97 Refigion, 266 REMAK, germinal continuity, 98 Repetition of stimuli, 122 Reversion, 151, 152 RIDDLE, 0., experiments, 121 Rodents, variation of, 76 RoENTGEN's rays, experiments

with, on germ-plasm, 127 RoMANEs, G. J., Darwin's con­

scientiousness, 36 Roux, \V., significance of mi-

tosis, 103

SAINT-HILAJRE, >129 Saltation, Darwin on, 165 Soorr, J ., letter from Darwin

to, 53 ScoTT, ,v. B., fossil record, 9;

quoted, 200, 213 Secretions; internal; IHl SEOOWJCK, A., friendship with

Darwin, 11; criticises Dar­win, 21

Seeds, origin of, 60; unadaptive characters in, 6!:!

Segregation, types of, 72; neces• sity of, 87

Selection, 216-2>!3, 244s; artifi­cial selection, limits to, 48; role of, 59-61; cessation of, 48, 174

Selective migration, 185, 190 Self-adjustment, 42 SEMON, R., on heredity, 39, ,l66 Sex, 10~ Shade foliage and heredity, 4'2 Sheep, isolation and develop-

ment of races, 74-76, 86 Sau·LL, G. H., 166, 197 Skull, 221

274 INDEX

Solutions, effect oo germ-plasm, 1$1-1$7

SP£>fCEn, H., 212, 263, 256; evolutionary teaching, 9

Sporophytes, origin of, 60 5-rANDFUSS, M., experiments, 123 &rARLnw, injection of fetus ex-

tract, 107 STRAsounoEn,. nucleus in hered-

ity, 99 Struggle for existence, 203 Sublime, feelings of, 35, 38 Swamping effects of intercross-

ing, 179

Teeth, 219, 2:32-234-, 241,242, 248 Temperature, check on migra­

tion, 186 TENNYSON, A., the struggle for

existence, 14-15 Teratological characters, 173 Testic extract, effect of, in-

jected, 107 Thy1·oid extract, effect of, 107 Titanotheres, 24-2-249 TowER, W. L., modification of

germ-cells, 110, Hl5-127, 197 T scHERMAK, E. v., rediscoverer

of Mendelism, 145 TYNDALL, J ., effect of Orig·in,.

54

Unit characters, 143-159; and mutation, 160, 161

Use and disuse, inheritance of, 35

Variability, somatic, in response to environment, 118

Variations, small, 217, 220, 222; large, 217

Vestiges of C,·eation, 31 VERWORM, 11'1., 261 VmcHow, R., germinal continu­

ity, 98 WAAGEN, W., 249; orthogenesis,

19S; mutation, 211, 229-233, 242; fossil series, 213

WAGNER, M., on jsolation, 72, 88, 89 ,v ALCOTT, C. 0., the fossil rec­ord, 9

WALKER, effect of testic extract, 107

, vALLACE, A. R., in New World, 7; natural selection, 18; ad­dress at Linnean Society's Anniversary, 19; coral reefs, 46; on isolation, 83

\V ABNEn, C. D., feeling of awe, 38

Wun, J. J., letter of Darwin to, 33

, vEsTwooo, J. 0., proposes read­er to combat Darwinism, 21

" 'EISMANN, A., 35, 40; under­mined Lamarc:k.ism, 10; non­transmissibility of acquired characters, 10, 11; idioplasm, 144; quoted, 161, 169, 183; adaptation, 193

Weismannism, 118 Wheat, limits to improvement,

118 'WHEELER, W . l\I., insect mu­

tants, 166 WHEWELL, Dr., excludes Origin

from college library, 91 WH1TMAN, C. O., orthogenesis,

193 ,VtEDERSHEUt, R., 261 ,viJJ, method of investigating

the, !l5Q Wn.so><, E. B., address by, 9:2-

ll3; on chromosomes, 129 WALLASTON', on wingless oceanic

beetles, 47 ,vooDWARD, s., 2Sl9 \VRTG>l'T, C., defense of Darwin,

8; review of Mivart, 39-34 \\T UNDT, i?5J1,

X-rays, experiments with, on germ-plasm, un

ZtEHl:N, 259 Zoonomia, influence on La­

marck, 10